Light-emitting device and display device

ABSTRACT

A technique of manufacturing a display device with high productivity is provided. In addition, a high-definition display device with high color purity is provided. By adjusting the optical path length between an electrode having a reflective property and a light-emitting layer by the central wavelength of a wavelength range of light passing through a color filter layer, the high-definition display device with high color purity is provided without performing selective deposition of light-emitting layers. In a light-emitting element, a plurality of light-emitting layers emitting light of different colors are stacked. The closer the light-emitting layer is to the electrode having a reflective property, the longer the wavelength of light emitted from the light-emitting layer is.

TECHNICAL FIELD

One embodiment of the present invention relates to an electroluminescentdisplay device and a manufacturing method of the display device.

BACKGROUND ART

In recent years, an electroluminescent (also referred to as EL) displaydevice has attracted attention as a display device with reducedthickness and weight (i.e., so-called flat panel display).

Light-emitting elements using light-emitting materials emitting light ofdifferent colors are provided as light-emitting elements used in pixelsin an EL display device, so that full-color display can be performed.

For such an EL display device, a method is used in which selectivedeposition of light-emitting materials in a minute pattern is performedfor each pixel by an evaporation method using a metal mask.

However, a shape defect or emission defect might be caused to alight-emitting element due to contact of a metal mask, and ways toprevent the defects have been explored (e.g., Patent Document 1). PatentDocument 1 discloses a structure in which a spacer for supporting ametal mask is provided over a pixel electrode so that the metal mask andthe pixel electrode are not in contact with each other at the time ofevaporation.

REFERENCE

-   [Patent Document 1] Japanese Published Patent Application No.    2006-126817

DISCLOSURE OF INVENTION

A method in which selective deposition of light-emitting materials isperformed for each pixel has a complicated process; thus, yield orproductivity is difficult to increase.

An object of one embodiment of the present invention is to provide alight-emitting element with which a reduction in power consumption andan increase in productivity of a display device can be achieved.

An object of one embodiment of the present invention is to provide ahigh-definition display device with high color purity.

According to one embodiment of the present invention, the optical pathlength between an electrode having a reflective property and alight-emitting layer is adjusted by a central wavelength of a colorfilter layer, whereby a high-definition display device with high colorpurity is provided without performing selective deposition oflight-emitting layers. In a light-emitting element, a plurality oflight-emitting layers which emit light of different colors are stacked,and the closer the light-emitting layer is to an electrode having areflective property, the longer the wavelength of light emitted from thelight-emitting layer is. Specifically, structures described below areemployed, for example.

One embodiment of the present invention is a display device whichincludes a first pixel including a first color filter layer and a secondpixel including a second color filter layer. The first pixel includes, afirst light-emitting element including a first electrode having areflective property. The second pixel includes a second light-emittingelement including a second electrode having a reflective property. Thefirst light-emitting element and the second light-emitting elementincludes, over the respective first and second electrodes havingreflective properties, a first light-emitting layer, a charge generationlayer, a second light-emitting layer, and an electrode having alight-transmitting property which are stacked in this order. In thefirst pixel, the optical path length between the first electrode havinga reflective property and the first light-emitting layer is one-quarterof the central wavelength of a wavelength range of light passing throughthe first color filter layer. In the second pixel, the optical pathlength between the second electrode having a reflective property and thesecond light-emitting layer is m-quarters (m is an odd number of threeor more), preferably three-quarters of the central wavelength of awavelength range of light passing through the second color filter layer.The central wavelength of the wavelength range of light passing throughthe first color filter layer is longer than the central wavelength ofthe wavelength range of light passing through the second color filterlayer.

In the above structure, the wavelength of a color of light emitted fromthe first light-emitting layer is longer than the wavelength of a colorof light emitted from the second light-emitting layer. Further, thesecond light-emitting element may include a conductive layer having alight-transmitting property between the second electrode having areflective property and the first light-emitting layer.

One embodiment of the present invention is a display device whichincludes a first pixel including a first color filter layer, a secondpixel including a second color filter layer, and a third pixel includinga third color filter layer. The first pixel includes a firstlight-emitting element including a first electrode having a reflectiveproperty. The second pixel includes a second light-emitting elementincluding a second electrode having a reflective property. The thirdpixel includes a third light-emitting element including a thirdelectrode having a reflective property. The first light-emittingelement, the second light-emitting element, and the third light-emittingelement include, over the respective first, second, and third electrodeshaving reflective properties, a first light-emitting layer, a chargegeneration layer, a second light-emitting layer, a third light-emittinglayer, and an electrode having a light-transmitting property which arestacked in this order. In the first pixel, the optical path lengthbetween the first electrode having a reflective property and the firstlight-emitting layer is one-quarter of the central wavelength of awavelength range of light passing through the first color filter layer.In the second pixel, the optical path length between the secondelectrode having a reflective property and the second light-emittinglayer is m-quarters (m is an odd number of three or more), preferablythree-quarters of the central wavelength of a wavelength range of lightpassing through the second color filter layer. In the third pixel, theoptical path length between the third electrode having a reflectiveproperty and the third light-emitting layer is n-quarters (n is an oddnumber of three or more), preferably five-quarters of the centralwavelength of a wavelength range of light passing through the thirdcolor filter layer. The central wavelength of the wavelength range oflight passing through the first color filter layer is longer than thecentral wavelength of the wavelength range of light passing through thesecond color filter layer. The central wavelength of the wavelengthrange of light passing through the second color filter layer is longerthan the central wavelength of the wavelength range of light passingthrough the third color filter layer.

In the above structure, the wavelength of a color of light emitted fromthe first light-emitting layer is longer than the wavelength of a colorof light emitted from the second light-emitting layer; the wavelength ofa color of light emitted from the second light-emitting layer is longerthan the wavelength of a color of light emitted from the thirdlight-emitting layer. Further, the second light-emitting element mayinclude a conductive layer having a light-transmitting property betweenthe second electrode having a reflective property and the firstlight-emitting layer; the third light-emitting element may include aconductive layer having a light-transmitting property between the thirdelectrode having a reflective property and the first light-emittinglayer. The conductive layer having a light-transmitting propertyincluded in the second light-emitting element may have a thicknessdifferent from that of the conductive layer having a light-transmittingproperty included in the third light-emitting element.

According to one embodiment of the present invention, a display devicecan be manufactured with high productivity.

According to one embodiment of the present invention, a high-definitiondisplay device can be provided.

Further, according to one embodiment of the present invention, a displaydevice with low power consumption can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A, 1B1, and 1B2 are views each illustrating a display device.

FIGS. 2A, 2B1, 2B2, and 2B3 are views each illustrating a displaydevice.

FIG. 3 is a view illustrating a display device.

FIGS. 4A and 4B are views illustrating a display device.

FIGS. 5A to 5F are views each illustrating an example of application ofa display device.

FIG. 6 is a view illustrating a structure of a light-emitting elementused in Example.

FIG. 7 is a graph showing the relation between wavelengths andtransmittance of color filter layers used in Example.

FIG. 8 is a graph showing characteristics of a display devicemanufactured in Example.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to theaccompanying drawings. Note that the present invention is not limited tothe following description, and it will be easily understood by thoseskilled in the art that various changes and modifications can be madewithout departing from the spirit and scope of the present invention.Therefore, the present invention should not be construed as beinglimited to the description of the embodiments below. In the structuresto be given below, the same portions or portions having similarfunctions are denoted by the same reference numerals in differentdrawings, and explanation thereof will not be repeated.

(Embodiment 1)

In this embodiment, one embodiment of an EL display device will bedescribed with reference to FIGS. 1A and 1B, FIGS. 2A, 2B1, 2B2, and2B3, and FIGS. 3A to 3C.

FIG. 1A is a cross-sectional view of a display portion in a displaydevice of this embodiment. FIGS. 1B1 and 1B2 are enlarged views of partof the cross-sectional view of FIG. 1A.

The display device illustrated in FIG. 1A includes a first pixel 130 aand a second pixel 130 b. The first pixel 130 a includes a firstlight-emitting element 132 a provided over a substrate 100 and a firstcolor filter layer 134 a provided for a counter substrate 128 in aregion overlapping with the first light-emitting element 132 a. Thesecond pixel 130 b includes a second light-emitting element 132 bprovided over the substrate 100 and a second color filter layer 134 bprovided for the counter substrate 128 in a region overlapping with thesecond light-emitting element 132 b.

In the display device illustrated in FIG. 1A, the first color filterlayer 134 a and the second color filter layer 134 b transmit light withdifferent wavelengths. The central wavelength of the wavelength range oflight passing through the first color filter layer 134 a and the centralwavelength of the wavelength range of light passing through the secondcolor filter layer 134 b are made to be different from each other,whereby a display device capable of multicolor display can be obtained.In this embodiment, the case where the central wavelength of thewavelength range of light passing through the first color filter layer134 a (hereinafter, also referred to as λ1) is longer than the centralwavelength of the wavelength range of light passing through the secondcolor filter layer 134 b (hereinafter, also referred to as λ2) will bedescribed as an example.

Note that in this specification, the term “central wavelength” refers tothe central wavelength of a wavelength range of light passing through acolor filter layer (preferably, a wavelength range of a transmittance of50% or more) in the visible light range (380 nm to 680 nm). For example,in the case where a red color filter layer transmits light in thewavelength range of 600 nm to 680 nm, the central wavelength is 640 nm.In the case where a green color filter layer transmits light in thewavelength range of 510 nm to 590 nm, the central wavelength is 550 nm.In the case where a blue color filter layer transmits light in thewavelength range of 380 nm to 520 nm, the central wavelength is 450 nm.

Note that a blue color filter layer and a green color filter layer eachhave an absorption spectrum in the long wavelength region around 700 nmin some cases.

However, the absorption spectrum in the above long wavelength regiondoes not affect the luminosity; therefore, the absorption spectrum inthe region is excluded. Thus, the visible light region in thisspecification and the like is a region with a wavelength of 680 nm orless.

The first light-emitting element 132 a and the second light-emittingelement 132 b respectively include a first electrode 102 a having areflective property and a second electrode 102 b having a reflectiveproperty which are placed with a distance therebetween over thesubstrate 100. The first light-emitting element 132 a and the secondlight-emitting element 132 b are electrically insulated from each otherby an insulating layer 126.

The first light-emitting element 132 a includes a first conductive layer104 a having a light-transmitting property, a first EL layer 106, acharge generation layer 108, a second EL layer 110, and an electrode 112having a light-transmitting property which are stacked in this orderover the first electrode 102 a having a reflective property. The secondlight-emitting element 132 b includes a second conductive layer 104 bhaving a light-transmitting property, the first EL layer 106, the chargegeneration layer 108, the second EL layer 110, and the electrode 112having a light-transmitting property which are stacked in this orderover the second electrode 102 b having a reflective property. In thisembodiment, light emitted from the first light-emitting element 132 aand the second light-emitting element 132 b is extracted from theelectrode 112 side.

Note that the first EL layer 106, the charge generation layer 108, thesecond EL layer 110, and the electrode 112 having a light-transmittingproperty are used in both the first light-emitting element 132 a and thesecond light-emitting element 132 b and are each formed as a continuousfilm.

FIG. 1B1 is an enlarged view of the first light-emitting element 132 a.FIG. 1B2 is an enlarged view of the second light-emitting element 132 b.

In FIGS. 1B1 and 1B2, the first light-emitting element 132 a and thesecond light-emitting element 132 b each include the first EL layer 106including at least a first light-emitting layer 120 and the second ELlayer 110 including at least a second light-emitting layer 122. Notethat each of the first EL layer 106 and the second EL layer 110 can havea stacked-layer structure including functional layers such as ahole-injection layer, a hole-transport layer, an electron-transportlayer, and an electron-injection layer, in addition to thelight-emitting layer.

The first conductive layer 104 a having a light-transmitting propertyand the second conductive layer 104 b having a light-transmittingproperty, which has a different thickness from the first conductivelayer 104 a having a light-transmitting property are included in thefirst light-emitting element 132 a and the second light-emitting element132 b, respectively; therefore, the total thickness of the firstlight-emitting element 132 a and the total thickness of the secondlight-emitting element 132 b are different.

The first conductive layer 104 a having a light-transmitting propertyhas a function of adjusting the optical path length of light which isemitted from the first light-emitting layer 120 and reflected back bythe first electrode 102 a having a reflective property (the light isalso referred to as first reflected light) by adjusting the thickness ofthe first conductive layer 104 a having a light-transmitting property.The first reflected light interferes with light entering the first colorfilter layer 134 a directly from the first light-emitting layer 120 (thelight is also referred to as first entering light). Thus, the phases ofthe first entering light and the first reflected light are aligned byadjusting the thickness of the first conductive layer 104 a having alight-transmitting property, whereby light emitted from the firstlight-emitting layer 120 can be amplified. Thus, the luminance of thelight-emitting element according to this embodiment is higher than theluminance of a light-emitting element in which the optical path lengthis not adjusted, in the case where the same current is applied to theselight-emitting elements. In addition, the phases of the first enteringlight and the first reflected light are aligned with the centralwavelength of the wavelength range of light passing through the firstcolor filter layer 134 a, whereby the color purity of light extractedfrom the first pixel 130 a can be increased.

The second conductive layer 104 b having a light-transmitting propertyhas a function of adjusting the optical path length of light which isemitted from the second light-emitting layer 122 and reflected back bythe second electrode 102 b having a reflective property (the light isalso referred to as second reflected light) by adjusting the thicknessof the second conductive layer 104 b having a light-transmittingproperty. The second reflected light interferes with light entering thesecond color filter layer 134 b directly from the second light-emittinglayer 122 (the light is also referred to as second entering light).Thus, the phases of the second entering light and the second reflectedlight are aligned by adjusting the thickness of the second conductivelayer 104 b having a light-transmitting property, whereby light emittedfrom the second light-emitting layer 122 can be amplified. Thus, theluminance of the light-emitting element according to this embodiment ishigher than the luminance of a light-emitting element in which theoptical path length is not adjusted, in the case where the same currentis applied to these light-emitting elements. In addition, the phases ofthe second entering light and the second reflected light are alignedwith the central wavelength of the wavelength range of light passingthrough the second color filter layer 134 b, whereby the color purity oflight extracted from the second pixel 130 b can be increased.

Specifically, it is preferable that the optical path length between thefirst electrode 102 a having a reflective property and the firstlight-emitting layer 120 in the first light-emitting element 132 aincluded in the first pixel 130 a be one-quarter of the centralwavelength of the wavelength range of light passing through the firstcolor filter layer 134 a (λ1). Moreover, it is preferable that theoptical path length between the second electrode 102 b having areflective property and the second light-emitting layer 122 in thesecond light-emitting element 132 b included in the second pixel 130 bbe three-quarters of the central wavelength of the wavelength range oflight passing through the second color filter layer 134 b (λ2).

More strictly, the optical path length between the first electrode 102 ahaving a reflective property and the first light-emitting layer 120 canalso be referred to as the optical path length between the firstelectrode 102 a having a reflective property and a light-emitting regionin the first light-emitting layer 120. Note that it is difficult tostrictly determine the position of the light-emitting region in alight-emitting layer and that the effects described above can besufficiently obtained by assuming any position in the light-emittinglayer as the position of the light-emitting region. In other words, theoptical path length between the first electrode 102 a having areflective property and the first light-emitting layer 120 can bereferred to as the optical path length between a surface of the firstelectrode 102 a having a reflective property and a lower surface of thefirst light-emitting layer 120 or more and the optical path lengthbetween the surface of the first electrode 102 a having a reflectiveproperty and an upper surface of the first light-emitting layer 120 orless. The same can be applied to the optical path length between thesecond electrode 102 b having a reflective property and the secondlight-emitting layer 122, and the optical path length between the thirdelectrode 102 c having a reflective property and the thirdlight-emitting layer 124, which will be described later.

Further, the spectrum of light emitted from the first light-emittinglayer 120 preferably has a peak in the wavelength region exhibiting thesame color as the central wavelength of the wavelength range of lightpassing through the first color filter layer 134 a. For example, in thecase where the first color filter layer 134 a has a central wavelengthin the red region (e.g., the case where the central wavelength is 690nm), the spectrum of light emitted from the first light-emitting layer120 preferably has a peak in the range of 600 nm to 700 nm.

In a similar manner, the spectrum of light emitted from the secondlight-emitting layer 122 preferably has a peak in the wavelength regionexhibiting the same color as the central wavelength of the wavelengthrange of light passing through the second color filter layer 134 b. Forexample, in the case where the second color filter layer 134 b has acentral wavelength in the green region (e.g., the case where the centralwavelength is 550 nm), the spectrum of light emitted from the secondlight-emitting layer 122 preferably has a peak in the range of 520 nm to550 nm.

Note that in this embodiment, the central wavelength of the wavelengthrange of light passing through the first color filter layer 134 a islonger than the central wavelength of the wavelength range of lightpassing through the second color filter layer 134 b; therefore, it ispreferable that the wavelength of a color of light emitted from thefirst light-emitting layer 120 be longer than the wavelength of a colorof light emitted from the second light-emitting layer 122.

Further, in the first light-emitting element 132 a, the optical pathlength between the first electrode 102 a having a reflective propertyand the first light-emitting layer 120 is set to one-quarter of thecentral wavelength of the wavelength range of light passing through thefirst color filter layer 134 a (λ1), the optical path length between thesecond light-emitting layer 122 and the electrode 112 having alight-transmitting property is set to one-quarter of the centralwavelength of the wavelength range of light passing through the secondcolor filter layer 134 b (λ2), and the optical path length between thefirst electrode 102 a having a reflective property and the electrode 112having a light-transmitting property is set to one-half of the centralwavelength of the wavelength range of light passing through the firstcolor filter layer 134 a (λ1), whereby a cavity effect can be obtained.

By setting the first light-emitting element 132 a under the aboveconditions, even in the second light-emitting element 132 b in which theoptical path length between the second electrode 102 b having areflective property and the second light-emitting layer 122 isthree-quarters of the central wavelength (λ2) of the second color filterlayer 134 b, the optical path length between the second light-emittinglayer 122 and the electrode 112 having a light-transmitting propertybecomes one-quarter of the central wavelength (λ2) of the second colorfilter layer 134 b and the optical path length between the secondelectrode 102 b having a reflective property and the electrode 112having a light-transmitting property becomes the central wavelength (λ2)of the second color filter layer 134 b. Thus, a cavity effect can beobtained. The color purity is further improved by the cavity effect.

The structure of the display device illustrated in FIG. 1A will bedescribed below along with specific materials. Note that an elementstructure, a manufacturing method, and the like described here are justexamples, and other known structures, materials, and manufacturingmethods can be applied without departing from the purpose of thisembodiment.

Plastic (an organic resin), glass, quartz, or the like can be used forthe substrate 100. As an example of plastic, a member made ofpolycarbonate, polyarylate, polyethersulfone, or the like can be given.Plastic is preferably used for the substrate 100, in which case areduction in the weight of the display device can be achieved.Alternatively, a sheet with a high barrier property against water vaporand a high heat radiation property (e.g., a sheet including diamond likecarbon (DLC)) can be used for the substrate 100.

Although not illustrated, a structure in which an inorganic insulator isprovided over the substrate 100 may be employed. The inorganic insulatorfunctions as a protective layer or a sealing film which blocks anexternal contaminant such as water. By providing the inorganicinsulator, deterioration of the light-emitting element can besuppressed; thus, the durability and lifetime of the display device canbe improved.

A single layer or a stack of a nitride film and a nitride oxide film canbe used as the inorganic insulator. Specifically, the inorganicinsulator can be formed using silicon oxide, silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride, orthe like by a CVD method, a sputtering method, or the like depending onthe material. It is preferable that the inorganic insulator be formedusing silicon nitride by a CVD method. The thickness of the inorganicinsulator may be greater than or equal to 100 nm and less than or equalto 1 p.m. Alternatively, an aluminum oxide film, a DLC film, a carbonfilm containing nitrogen, or a film containing zinc sulfide and siliconoxide (ZnS.SiO₂ film) may be used as the inorganic insulator.

Alternatively, a thin glass substrate can be used as the inorganicinsulator. For example, a glass substrate with a thickness greater thanor equal to 30 μm and less than or equal to 100 μm can be used.

A metal plate may be provided on a bottom surface of the substrate 100(a surface opposite to the surface over which the light-emitting elementis provided). In the case where an inorganic insulator is provided, ametal plate may be used instead of the substrate 100. Although there isno particular limitation on the thickness of the metal plate, a metalplate with a thickness greater than or equal to 10 μm and less than orequal to 200 μm is preferably used, in which case a reduction in theweight of the display device can be achieved. Further, although there isno particular limitation on the material of the metal plate, a metalsuch as aluminum, copper, or nickel, a metal alloy such as an aluminumalloy or stainless steel, or the like can be preferably used.

The metal plate and the substrate 100 can be bonded to each other withan adhesive layer. As the adhesive layer, a visible light curableadhesive, an ultraviolet curable adhesive, or a thermosetting adhesivecan be used. As examples of materials of such adhesives, an epoxy resin,an acrylic resin, a silicone resin, a phenol resin, and the like can begiven. A moisture-absorbing substance serving as a desiccant may becontained in the adhesive layer.

A metal plate has low permeability; thus, by providing the metal plate,the entry of moisture into the light-emitting element can be prevented.Consequently, by providing the metal plate, a highly reliable displaydevice in which deterioration due to moisture is suppressed can beprovided.

The first electrode 102 a having a reflective property and the secondelectrode 102 b having a reflective property are provided opposite tothe side where light is extracted and is &Lined using a material havinga reflective property. As the material having a reflective property, ametal material such as aluminum, gold, platinum, silver, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium canbe used. In addition, any of the following can be used: alloyscontaining aluminum (aluminum alloys) such as an alloy of aluminum andtitanium, an alloy of aluminum and nickel, and an alloy of aluminum andneodymium; and an alloy containing silver such as an alloy of silver andcopper. An alloy of silver and copper is preferable because of its highheat resistance. Further, a metal film or a metal oxide film is stackedon an aluminum alloy film, whereby oxidation of the aluminum alloy filmcan be prevented. As examples of a material of the metal film or themetal oxide film, titanium, titanium oxide, and the like are given. Theabove materials are preferable because they are present in large amountsin the Earth's crust and inexpensive to achieve a reduction inmanufacturing cost of a light-emitting element.

In this embodiment, the case where the first electrode 102 a having areflective property and the second electrode 102 b having a reflectiveproperty are used as an anode of the light-emitting element is describedas an example. However, one embodiment of the present invention is notlimited thereto.

The first conductive layer 104 a having a light-transmitting propertyand the second conductive layer 104 b having a light-transmittingproperty are formed of a single layer or stacked layers using a materialhaving a property of transmitting visible light. As the material havinglight-transmitting property, for example, indium oxide, indium tinoxide, an indium oxide-zinc oxide alloy, zinc oxide, zinc oxide to whichgallium is added, graphene, or the like can be used.

The conductive layer having a light-transmitting property can be formedusing a conductive composition containing a conductive high molecule(also referred to as conductive polymer). As the conductive highmolecule, a so-called π-electron conjugated conductive polymer can beused. For example, polyaniline or a derivative thereof, polypyrrole or aderivative thereof, polythiophene (PEDOT) or a derivative thereof, acopolymer of two or more of aniline, pyrrole, and thiophene or aderivative thereof, and the like can be given.

Note that the first electrode 102 a having a reflective property, thesecond electrode 102 b having a reflective property, the firstconductive layer 104 a having a light-transmitting property, and thesecond conductive layer 104 b having a light-transmitting property canbe processed into a desired shape in a photolithography step and anetching step. Thus, a minute pattern can be formed with goodcontrollability, which makes it possible to obtain a high-definitiondisplay device.

Further, when the first conductive layer 104 a having alight-transmitting property and the second conductive layer 104 b havinga light-transmitting property are provided independently in each pixel,crosstalk can be prevented even in the case where the thickness of theconductive layer having a light-transmitting property is extremely largeor the case where the conductivity of the conductive layer having alight-transmitting property is high.

An insulating layer 126 having openings is formed over the firstconductive layer 104 a having a light-transmitting property and thesecond conductive layer 104 b having a light-transmitting property. Thefirst EL layer 106 is in contact with the first conductive layer 104 ahaving a light-transmitting property and the second conductive layer 104b having a light-transmitting property through the openings. Theinsulating layer 126 is foamed using an organic insulating material suchas polyimide, acrylic, polyamide, or epoxy, or an inorganic insulatingmaterial. It is particularly preferable that the insulating layer 126 beformed using a photosensitive resin material to have an opening overeach of the first conductive layer 104 a having a light-transmittingproperty and the second conductive layer 104 b having alight-transmitting property so that the sidewall of the opening isformed to have a tilted surface with continuous curvature. Theinsulating layer 126 may be tapered or inversely tapered.

The first EL layer 106 may include at least the first light-emittinglayer 120. In addition, the first EL layer 106 can have a stacked-layerstructure in which a layer containing a substance having a highhole-transport property, a layer containing a substance having a highelectron-transport property, a layer containing a substance having ahigh hole-injection property, a layer containing a substance having ahigh electron-injection property, a layer containing a bipolar substance(a substance having a high hole-transport and electron-transportproperties), and the like are combined as appropriate. For example, thefirst EL layer 106 can have a stacked-layer structure including ahole-injection layer, a hole-transport layer, the first light-emittinglayer 120, an electron-transport layer, and an electron-injection layer.Needless to say, in the case where the first electrode 102 a having areflective property and the second electrode 102 b having a reflectiveproperty are used as a cathode, a stacked-layer structure in which anelectron-injection layer, an electron-transport layer, the firstlight-emitting layer 120, a hole-transport layer, and a hole-injectionlayer are stacked in this order from the cathode side may be employed.

The hole-injection layer is a layer containing a substance having a highhole-injection property. As the substance having a high hole-injectionproperty, for example, metal oxides such as molybdenum oxide, titaniumoxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromium oxide,zirconium oxide, hafnium oxide, tantalum oxide, silver oxide, tungstenoxide, and manganese oxide can be used. A phthalocyanine-based compoundsuch as phthalocyanine (abbreviation: H₂Pc), or copper(II)phthalocyanine (abbreviation: CuPc) can also be used.

Any of the following aromatic amine compounds which are low molecularorganic compounds can also be used:4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2), and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1).

Any of the high molecular compounds (e.g., oligomers, dendrimers, orpolymers) can also be used. Examples of the high molecular compoundinclude poly(N-vinylcarbazole) (abbreviation: PVK)poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD). A high molecular compound to which acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS)or polyaniline/poly(styrenesulfonic acid) (PAni/PSS), can also be used.

In particular, it is preferable to use a composite material in which anacceptor substance is mixed with an organic compound having a highhole-transport property for the hole-injection layer. With the use ofthe composite material in which an acceptor substance is mixed with asubstance having a high hole-transport property, excellent holeinjection from the anode can be obtained, which results in a reductionin the driving voltage of the light-emitting element. Such a compositematerial can be formed by co-evaporation of a substance having a highhole-transport property and a substance having an acceptor property.When the hole-injection layer is formed using the composite material,holes are easily injected into the first EL layer 106 from the anode.

As the organic compound for the composite material, a variety ofcompounds such as an aromatic amine compound, carbazole derivatives,aromatic hydrocarbon, and a high molecular compound (such as oligomer,dendrimer, or polymer) can be used. The organic compound used for thecomposite material is preferably an organic compound having a highhole-transport property. Specifically, a substance having a holemobility of 10⁻⁶ cm²/Vs or higher is preferably used. Note that anyother substances may also be used as long as the hole-transport propertythereof is higher than the electron-transport property thereof. Specificexamples of the organic compound that can be used for the compositematerial will be given below.

As the organic compound that can be used for the composite material, anyof the following can be used: aromatic amine compounds such as TDATA,MTDATA, DPAB, DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), and4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP),and carbazole derivatives, such as 4,4′-di(N-carbazolyl)biphenyl(abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene(abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA),9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

Any of the following aromatic hydrocarbon compounds can also be used:2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),9,10-bis[2-(1-naphthyl)phenyl)-2-tert-butylanthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene.

Any of the following aromatic hydrocarbon compounds can also be used:2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene,pentacene, coronene, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation:DPVBi), or 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene(abbreviation: DPVPA).

Examples of the electron acceptor include organic compounds such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ) and chloranil; and transition metal oxides. Other examplesinclude oxides of metals belonging to Groups 4 to 8 in the periodictable. Specifically, vanadium oxide, niobium oxide, tantalum oxide,chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, andrhenium oxide are preferable because of their high electron-acceptingproperties. Among these, molybdenum oxide is particularly preferablebecause it is stable in the air, has a low hygroscopic property, and iseasily handled.

Note that the hole injection layer may be formed using a compositematerial of the high molecular compound such as PVK, PVTPA, PTPDMA, orPoly-TPD, and the electron acceptor.

Note that in the case where a layer containing the above compositematerial is provided in the first EL layer 106, the optical path lengthof the first reflected light may be adjusted by adjusting the thicknessof the layer containing the above composite material. In that case, thefirst conductive layer 104 a having a light-transmitting property is notnecessarily provided.

The hole-transport layer is a layer containing a substance having a highhole-transport property. As the substance having a high hole-transportproperty, any of the following aromatic amine compounds can be used, forexample: NPB, TPD, BPAFLP,4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). The substances given here are mainly ones having ahole mobility of 10⁻⁶ cm²/Vs or higher. However, any other substancesmay also be used as long as the hole-transport property thereof ishigher than the electron-transport property thereof. The layercontaining a substance having a high hole-transport property is notlimited to a single layer, and may be a stack of two or more layerscontaining any of the above substances.

A carbazole derivative such as CBP, CzPA, or PCzPA or an anthracenederivative such as t-BuDNA, DNA, or DPAnth may be used for thehole-transport layer.

Alternatively, a high molecular compound such as PVK, PVTPA, PTPDMA, orPoly-TPD can be used for the hole-transport layer.

The first light-emitting layer 120 is a layer containing alight-emitting organic compound. As the light-emitting organic compound,for example, a fluorescent compound which emits fluorescence or aphosphorescent compound which emits phosphorescence can be used.

As the fluorescent compound that can be used for the firstlight-emitting layer 120, a material for blue light emission, a materialfor green light emission, a material for yellow light emission, and amaterial for red light emission are given. Examples of the material forblue light emission includeN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA), and4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA). Example of the material for green light emissioninclude N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),N-[9,10-bis(1,1′-biphenyl-2-yl)]-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), and N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA). Examples of the material for yellow lightemission include rubrene and5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT).Examples of the material for red light emission includeN,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD) and7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD).

As the phosphorescent compound that can be used for the firstlight-emitting layer 120, a material for blue light emission, a materialfor green light emission, a material for yellow light emission, amaterial for orange light emission, a material for red light emissionare given. Examples of the material for blue light emission includebis[2-(4′,6′-difluorophenyl)pyridinato-N,C_(2′)]iridium(III)tetrakis(1-pyrazolyl)borate(abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinate(abbreviation: FIrpic),bis{2-[3′,5′-r-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate(abbreviation: Ir(CF₃ppy)₂(pic)), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate(abbreviation: FIr(acac)). Examples of the material for green lightemission include tris(2-phenylpyridinato-N,C^(2′))iridium(III)(abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(ppy)₂(acac)),bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate(abbreviation: Ir(pbi)₂(acac)),bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation:Ir(bzq)₂(acac)), and tris(benzo[h]quinolinato)iridium(III)(abbreviation: Ir(bzq)₃). Examples of the material for yellow lightemission includebis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis[2-(4′-(perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(bt)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)-5-methylpyrazinato]iridium(III)(abbreviation: Ir(Fdppr-Me)₂(acac)), and(acetylacetonato)bis{2-(4-methoxyphenyl)-3,5-dimethylpyrazinato}iridium(III)(abbreviation: Ir(dmmoppr)₂(acac)). Examples of the material for orangelight emission include tris(2-phenylquinolinato-N,C^(2′))iridium(III)(abbreviation: Ir(pq)₃),bis(2-phenylquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(pq)₂(acac)),(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)), and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)). Examples of the material for redlight emission include organometallic complexes such asbis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C^(3′))iridium(III)acetylacetonate(abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),(dipivaloylmethanato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(dpm)), and2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II)(abbreviation: PtOEP). In addition, rare earth metal complexes, such astris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:Tb(acac)₃(Phen)),tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)), andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)), exhibit light emission from rare earthmetal ions (electron transition between different multiplicities), andthus can be used as phosphorescent compounds.

Note that the first light-emitting layer 120 may have a structure inwhich any of the above light-emitting organic compounds (a guestmaterial) is dispersed in another substance (a host material). As a hostmaterial, various kinds of materials can be used, and it is preferableto use a substance which has a lowest unoccupied molecular orbital level(LUMO level) higher than the light-emitting substance and has a highestoccupied molecular orbital level (HOMO level) lower than that of thelight-emitting substance.

As the host material, specifically, any of the following can be used:metal complexes such as tris(8-quinolinolato)aluminum(III)(abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(III)(abbreviation: Almq₃), bis(10-hydroxybenzo[h]quinolinato)beryllium(II)(abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ);heterocyclic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)-(abbreviation:TPBI), bathophenanthroline (abbreviation: BPhen), and bathocuproine(BCP); condensed aromatic compounds such as9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,9′-bianthryl (abbreviation: BANT),9,9′-(stilbene-3,3′-diyl)diphenanthrene (abbreviation: DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2),3,3′,3″-(benzene-1,3,5-triyl)tripyrene (abbreviation: TPB3),9,10-diphenylanthracene (abbreviation: DPAnth), and6,12-dimethoxy-5,11-diphenylchrysene; and aromatic amine compounds suchas N,N-dipheyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine(abbreviation: DPhPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA),N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(abbreviation: PCAPBA),N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA), NPB, TPD, DFLDPBi, and BSPB.

Plural kinds of materials can be used as the host material. For example,in order to suppress crystallization, a substance such as rubrene whichsuppresses crystallization, may be further added. In addition, NPB, Alq,or the like may be further added in order to efficiently transfer energyto the guest material.

When the structure in which a guest material is dispersed in a hostmaterial is employed, crystallization of the first light-emitting layer120 can be suppressed. In addition, concentration quenching due to highconcentration of the guest material can be suppressed.

A high molecular compound can be used for the first light-emitting layer120. As specific examples of the high molecular compound, a material forblue light emission, a material for green light emission, and a materialfor orange to red light emission are given. Examples of the material forblue light emission include poly(9,9-dioctylfluorene-2,7-diyl)(abbreviation: PFO),poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,5-dimethoxybenzene-1,4-diyl)](abbreviation: PF-DMOP), andpoly{(9,9-dioctylfluorene-2,7-diyl)-co-[N,N′-di-(p-butylphenyl)-1,4-diaminobenzene]}(abbreviation: TAB-PFH). Examples of the material for green lightemission include poly(p-phenylenevinylene) (abbreviation: PPV),poly[(9,9-dihexylfluorene-2,7-diyl)-alt-co-(benzo[2,1,3]thiadiazole-4,7-diyl)](abbreviation:PFBT), andpoly[(9,9-dioctyl-2,7-divinylenfluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)].Examples of the material for orange to red light emission includepoly[2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylenevinylene](abbreviation:MEH-PPV), poly(3-butylthiophene-2,5-diyl) (abbreviation: R4-PAT),poly{[9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenylene]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}, andpoly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-bis(1-cyanovinylenephenylene)]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}(abbreviation: CN-PPV-DPD).

Note that the first EL layer 106 may have a structure including two ormore light-emitting layers.

The electron-transport layer is a layer containing a substance having ahigh electron-transport property. As the substance having a highelectron-transport property, any of the following can be used, forexample: metal complexes having a quinoline skeleton or a benzoquinolineskeleton, such as tris(8-quinolinolato)aluminum (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂), andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq). A metal complex or the like including an oxazole-based orthiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(abbreviation: Zn(BOX)₂) or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc(abbreviation: Zn(BTZ)₂) can also be used. Other than the metalcomplexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(abbreviation: PBD),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can also be used. Thesubstances given here are mainly ones having an electron mobility of10⁻⁶ cm²/Vs or higher. The electron-transport layer is not limited to asingle layer and may be a stack of two or more layers containing any ofthe above substances.

The electron-injection layer is a layer containing a substance having ahigh electron-injection property. For the electron-injection layer, analkali metal, an alkaline-earth metal, or a compound thereof, such aslithium, cesium, calcium, lithium fluoride, cesium fluoride, calciumfluoride, or lithium oxide, can be used. Alternatively, a rare earthmetal compound such as erbium fluoride can be used. Furtheralternatively, any of the above substances for forming theelectron-transport layer can be used.

Charges are generated in the charge generation layer 108 by applyingvoltage to the light-emitting element. The charge generation layer 108has functions of injecting holes into the EL layer on the cathode sideand injecting electrons into the EL layer on the anode side.

The charge generation layer 108 can be formed using the above compositematerial. The charge generation layer 108 may have a stacked-layerstructure including a layer containing the composite material and alayer containing another material. In that case, as the layer containinganother material, a layer containing an electron donating substance anda substance with high electron-transport properties, a layer formed of atransparent conductive film, or the like can be used. As for alight-emitting element having such a structure, problems such as energytransfer and quenching occur with difficulty, and a light-emittingelement which has both high light emission efficiency and long lifetimecan be easily obtained due to expansion in the choice of materials.Moreover, a light-emitting element which provides phosphorescence fromone EL layer and fluorescence from another EL layer can be easilyobtained.

When the charge generation layer is provided between the stacked ELlayers as illustrated in FIGS. 1A, 1B1, and 1B2, the element can havehigh luminance and long lifetime while the current density is kept low.In addition, a voltage drop due to the resistance of the electrodematerial can be reduced, whereby uniform light emission in a large areais possible.

The second EL layer 110 may include at least the second light-emittinglayer 122. In addition, the second EL layer 110 can have a stacked-layerstructure in which a layer containing a substance having a highhole-transport property, a layer containing a substance having a highelectron-transport property, a layer containing a substance having ahigh hole-injection property, a layer containing a substance having ahigh electron-injection property, a layer containing a bipolar substance(a substance having a high hole-transport and electron-transportproperties), and the like are combined as appropriate. The second ELlayer 110 may have a structure similar to that of the first EL layer 106or may have a stacked-layer structure different from that of the firstEL layer 106. For example, the second EL layer 110 can have astacked-layer structure including a hole-injection layer, ahole-transport layer, the second light-emitting layer 122, anelectron-transport layer, an electron-injection buffer layer, anelectron-relay layer, and a composite material layer in contact with theelectrode 112 having a light-transmitting property. Note that the secondEL layer 110 may have a structure including two or more light-emittinglayers.

The composite material layer in contact with the electrode 112 having alight-transmitting property is preferably provided, in which case damagecaused to the second EL layer 110 particularly when the electrode 112having a light-transmitting property is formed by a sputtering methodcan be reduced. The composite material layer can be formed using theabove-described composite material in which an acceptor substance ismixed with an organic compound having a high hole-transport property.

Further, by providing the electron-injection buffer layer, an injectionbarrier between the composite material layer and the electron-transportlayer can be reduced; thus, electrons generated in the compositematerial layer can be easily injected into the electron-transport layer.

A substance having a high electron-injection property can be used forthe electron-injection buffer layer: for example, an alkali metal, analkaline earth metal, a rare earth metal, a compound of the above metal(e.g., an alkali metal compound (including an oxide such as lithiumoxide, a halide, or carbonate such as lithium carbonate or cesiumcarbonate), an alkaline earth metal compound (including an oxide, ahalide, or carbonate), or a rare earth metal compound (including anoxide, a halide, or carbonate).

In the case where the electron-injection buffer layer contains asubstance having a high electron-transport property and a donorsubstance, the donor substance is preferably added so that the massratio of the donor substance to the substance having a highelectron-transport property ranges from 0.001:1 to 0.1:1. Note that asthe donor substance, an organic compound such as tetrathianaphthacene(abbreviation: TTN), nickelocene, or decamethylnickelocene can be usedas well as an alkali metal, an alkaline earth metal, a rare earth metal,a compound of the above metal (e.g., an alkali metal compound (e.g., anoxide such as lithium oxide, a halide, and a carbonate such as lithiumcarbonate or cesium carbonate), an alkaline earth metal compound (e.g.,an oxide, a halide, and a carbonate), and a rare earth metal compound(e.g., an oxide, a halide, and a carbonate). Note that as the substancehaving a high electron-transport property, a material similar to thematerial for the electron-transport layer described above can be used.

Furthermore, it is preferable that the electron-relay layer be formedbetween the electron-injection buffer layer and the composite materiallayer. The electron-relay layer is not necessarily provided; however, byproviding the electron-relay layer having a high electron-transportproperty, electrons can be rapidly transported to the electron-injectionbuffer layer.

The structure in which the electron-relay layer is sandwiched betweenthe composite material layer and the electron-injection buffer layer isa structure in which the acceptor substance contained in the compositematerial layer and the donor substance contained in theelectron-injection buffer layer are less likely to interact with eachother; thus, their functions hardly interfere with each other.Therefore, an increase in the driving voltage can be prevented.

The electron-relay layer contains a substance having a highelectron-transport property and is formed so that the LUMO level of thesubstance having a high electron-transport property is located betweenthe LUMO level of the acceptor substance contained in the compositematerial layer and the LUMO level of the substance having a highelectron-transport property contained in the electron-transport layer.In the case where the electron-relay layer contains a donor substance,the donor level of the donor substance is controlled so as to be locatedbetween the LUMO level of the acceptor substance in the compositematerial layer and the LUMO level of the substance having a highelectron-transport property contained in the electron-transport layer.As a specific value of the energy level, the LUMO level of the substancehaving a high electron-transport property contained in theelectron-relay layer is preferably greater than or equal to −5.0 eV,more preferably greater than or equal to −5.0 eV and less than or equalto −3.0 eV.

It is preferable to use a phthalocyanine-based material or a metalcomplex having a metal-oxygen bond and an aromatic ligand as thesubstance having a high electron-transport property contained in theelectron-relay layer.

As the phthalocyanine-based material contained in the electron relaylayer, specifically, any of the following is preferably used: CuPc, aphthalocyanine tin(II) complex (SnPc), a phthalocyanine zinc complex(ZnPc), cobalt(II) phthalocyanine, β-form (CoPc), phthalocyanine iron(FePc), and vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine(PhO-VOPc).

As the metal complex having a metal-oxygen bond and an aromatic ligand,which is contained in the electron-relay layer, a metal complex having ametal-oxygen double bond is preferably used. The metal-oxygen doublebond has an acceptor property (a property of easily acceptingelectrons); thus, electrons can be transferred (donated and accepted)more easily. Further, the metal complex which has a metal-oxygen doublebond is considered stable. Thus, the use of the metal complex having themetal-oxygen double bond makes it possible to drive the light-emittingelement at low voltage more stably.

A phthalocyanine-based material is preferable as a metal complex havinga metal-oxygen bond and an aromatic ligand. Specifically, any of vanadylphthalocyanine (VOPc), a phthalocyanine tin(IV) oxide complex (SnOPc),and a phthalocyanine titanium oxide complex (TiOPc) is preferablebecause a metal-oxygen double bond is more likely to act on anothermolecular in terms of a molecular structure and an acceptor property ishigh.

Note that a phthalocyanine-based material having a phenoxy group ispreferable as the phthalocyanine-based materials described above.Specifically, a phthalocyanine derivative having a phenoxy group, suchas PhO-VOPc, is preferable. A phthalocyanine derivative having a phenoxygroup is soluble in a solvent. Thus, a phthalocyanine derivative has anadvantage of being easily handled during formation of the light-emittingelement and an advantage of facilitating maintenance of an apparatusused for forming a film.

The electron-relay layer may further contain a donor substance. As thedonor substance, any of the following can be used: an organic compoundsuch as tetrathianaphthacene (abbreviation: TTN), nickelocene, anddecamethylnickelocene, in addition to an alkali metal, an alkaline earthmetal, a rare earth metal, and a compound of the above metals (e.g., analkali metal compound (e.g., an oxide such as lithium oxide, a halide,and a carbonate such as lithium carbonate or cesium carbonate), analkaline earth metal compound (e.g., an oxide, a halide, and acarbonate), and a rare earth metal compound (e.g., an oxide, a halide,and a carbonate)). When such a donor substance is contained in theelectron-relay layer, electrons can be transferred easily and thelight-emitting element can be driven at lower voltage.

In the case where a donor substance is contained in the electron-relaylayer, in addition to the materials described above as the substancehaving a high electron-transport property, a substance having a LUMOlevel greater than the acceptor level of the acceptor substancecontained in the composite material layer can be used. Specifically, itis preferable to use a substance having a LUMO level of greater than orequal to −5.0 eV, preferably greater than or equal to −5.0 eV and lessthan or equal to −3.0 eV. As examples of such a substance, a perylenederivative and a nitrogen-containing condensed aromatic compound aregiven. Note that a nitrogen-containing condensed aromatic compound ispreferably used for the electron-relay layer because of its stability.

Specific examples of the perylene derivative include3,4,9,10-perylenetetracarboxylicdianhydride (abbreviation: PTCDA),3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (abbreviation:PTCBI), N,N-dioctyl-3,4,9,10-perylenetetracarboxylic diimide(abbreviation: PTCDI-C8H), andN,N′-dihexyl-3,4,9,10-perylenetetracarboxylic diimide (Hex PTC).

Specific examples of the nitrogen-containing condensed aromatic compoundinclude pirazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (PPDN),2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT(CN)₆),2,3-diphenylpyrido[2,3-b]pyrazine (2PYPR), and2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine (F2PYPR).

Other than the above, 7,7,8,8-tetracyanoquinodimethane (abbreviation:TCNQ), 1,4,5,8-naphthalenetetracarboxylicdianhydride (abbreviation:NTCDA), perfluoropentacene, copper hexadecafluoro phthalocyanine(abbreviation: F₁₆CuPc),N,N′-bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl)-1,4,5,8-naphthalenetetracarboxylic diimide (abbreviation: NTCDI-C8F),3′,4′-dibutyl-5,5″-bis(dicyanomethylene)-5,5″-dihydro-2,2′:5′,2″-terthiophene(abbreviation: DCMT), a methanofullerene (e.g., [6,6]-phenyl C₆₁ butyricacid methyl ester), or the like can be used.

Note that in the case where a donor substance is contained in theelectron-relay layer, the electron-relay layer may be formed by a methodsuch as co-evaporation of the substance having a high electron-transportproperty and the donor substance.

Each of the hole-injection layer, the hole-transport layer, the secondlight-emitting layer 122, and the electron-transport layer may be formedusing any of the materials given above. However, a light-emittingmaterial which emits light of a color with a wavelength shorter thanthat of a color of light emitted from the first light-emitting layer 120is preferably used as a light-emitting material for the secondlight-emitting layer 122.

The electrode 112 having a light-transmitting property is provided onthe side where light is extracted, and thus is formed using a materialhaving light-transmitting property. As the material havinglight-transmitting property, indium oxide, indium tin oxide, an indiumoxide-zinc oxide alloy, zinc oxide, zinc oxide to which gallium isadded, graphene, or the like can be used.

As the electrode 112 having a light-transmitting property, a metalmaterial such as gold, platinum, nickel, tungsten, chromium, molybdenum,iron, cobalt, copper, palladium, or titanium can be used. A nitride ofthe metal material (e.g., titanium nitride) or the like may be used. Inthe case of using the metal material (or the nitride thereof), theelectrode 112 having a light-transmitting property may be thinned so asto have a light-transmitting property.

The first EL layer 106, the charge generation layer 108, and the secondEL layer 110 in the first light-emitting element 132 a and the secondlight-emitting element 132 b are common in pixels and are each formed asa continuous film. Thus, selective deposition using a metal mask is notneeded in a manufacturing process, which makes it possible to performformation over a large area at one time and to increase the size andproductivity of a display device. Moreover, a display region in thedisplay portion can be enlarged. Furthermore, a defect due to the entryof particles, or the like, which occurs at the time of using a metalmask, can be prevented; thus, a display device can be manufactured witha high yield.

Note that an inorganic insulating film which covers the firstlight-emitting element 132 a and the second light-emitting element 132 bmay be provided. The inorganic insulating film serves as a protectivelayer or a sealing film which blocks an external contaminant such aswater. By providing the inorganic insulating film, the deterioration ofthe light-emitting element can be suppressed; thus, the durability andlifetime of the display device can be improved. A material similar tothe material of the inorganic insulator described above can be used as amaterial of the inorganic insulating film.

A moisture-absorbing substance which serves as a desiccant may beprovided between the substrate 100 and the counter substrate 128. Themoisture-absorbing substance may be provided in a solid state such aspowdery state or may be provided in a state of a film containing amoisture-absorbing substance over the first light-emitting element 132 aand the second light-emitting element 132 b by a film formation methodsuch as a sputtering method.

A material similar to that of the substrate 100 can be used for thecounter substrate 128. Note that the counter substrate 128 needs to havea property of transmitting light passing through at least the firstcolor filter layer 134 a and the second color filter layer 134 b.

For example, a chromatic color light-transmitting resin can be used asthe first color filter layer 134 a and the second color filter layer 134b. As the chromatic color light-transmitting resin, a photosensitiveorganic resin or a non-photosensitive organic resin can be used. Thephotosensitive organic resin is preferably used, in which case thenumber of resist masks can be reduced, which results in thesimplification of the process.

Chromatic colors are all colors except achromatic colors such as black,gray, and white. The color filter layer is formed using a material whichtransmits only light of the chromatic colors. As chromatic color, red,green, blue, or the like can be used. Alternatively, cyan, magenta,yellow, or the like may be used. “Transmitting only light of a chromaticcolor” means that light passing through the color filter layer has apeak at a wavelength of the light of the chromatic color.

The thickness of the color filter layer may be controlled to be optimalas appropriate in consideration of the relationship between theconcentration of a coloring material to be contained and thetransmittance of light. In the display device described in thisembodiment, the half width of a spectrum of light emitted from the firstlight-emitting layer 120 can be reduced by adjusting the optical pathlength between the first electrode 102 a having a reflective propertyand the first light-emitting layer 120 and by utilizing lightinterference. In a similar manner, the half width of a spectrum of lightemitted from the second light-emitting layer 122 can be reduced byadjusting the optical path length between the second electrode 102 bhaving a reflective property and the second light-emitting layer 122 andby utilizing light interference. Thus, the concentration of a coloringmaterial of the first color filter layer 134 a and the concentration ofa coloring material of the second color filter layer 134 b can be low.In addition, the thicknesses of the first color filter layer 134 a andthe second color filter layer 134 b can be small. As a result, lightabsorption by the first color filter layer 134 a or the second colorfilter layer 134 b can be reduced; thus, the use efficiency of light canbe improved.

The example in which the first color filter layer 134 a and the secondcolor filter layer 134 b are provided on the inner side of the countersubstrate 128 is described in this embodiment. However, one embodimentof the present invention is not limited thereto. The first color filterlayer 134 a and the second color filter layer 134 b can be provided onthe outer side of the counter substrate 128 (i.e., on the opposite sideto the light-emitting elements).

Alternatively, a light-transmitting resin layer with a chromatic colorwhich functions as a color filter layer may be formed over the firstlight-emitting element 132 a and the second light-emitting element 132b.

A light-blocking layer may be provided in a region between the firstcolor filter layer 134 a and the second color filter layer 134 b (i.e.,a region overlapping with the insulating layer 126). The light-blockinglayer is formed using a light-blocking material which reflects orabsorbs light. For example, a black organic resin can be used, which canbe formed by mixing a black resin of a pigment material, carbon black,titanium black, or the like into a resin material such as photosensitiveor non-photosensitive polyimide. Alternatively, a light-blocking metalfilm can be used, which is made of chromium, molybdenum, nickel,titanium, cobalt, copper, tungsten, aluminum, or the like, for example.

There is no particular limitation on the formation method of thelight-blocking layer, and a dry method such as an evaporation method, asputtering method, or a CVD method, or a wet method such as a spincoating method, a dip coating method, a spray coating method, a dropletdischarge method (e.g., ink jetting), a screen printing method, or anoffset printing method may be used depending on the material. If needed,an etching method (dry etching or wet etching) may be employed to form adesired pattern.

The light-blocking layer can prevent light from leaking to an adjacentpixel. Therefore, by providing the light-blocking layer, an image can bedisplayed with high contrast and high definition.

FIGS. 2A, 2B1, 2B2, and 2B3 illustrate one embodiment of a displaydevice which is different from the display device illustrated in FIGS.1A, 1B1, and 1B2. FIG. 2A is a cross-sectional view of a display portionin the display device. FIGS. 2B1, 2B2, and 2B3 are enlarged views ofpart of the cross-sectional view of FIG. 2A. The structure of thedisplay device illustrated in FIGS. 2A, 2B1, 2B2, and 2B3 is common withthe structure of the display device illustrated in FIGS. 1A, 1B1, and1B2 in many parts. Therefore, in the following description, the sameportions will not be described.

The display device illustrated in FIG. 2A includes a first pixel 230 a,a second pixel 230 b, and a third pixel 230 c. The first pixel 230 aincludes a first light-emitting element 232 a provided over thesubstrate 100 and the first color filter layer 134 a provided for thecounter substrate 128 in a region overlapping with the firstlight-emitting element 232 a. The second pixel 230 b includes a secondlight-emitting element 232 b provided over the substrate 100 and thesecond color filter layer 134 b provided for the counter substrate 128in a region overlapping with the second light-emitting element 232 b.The third pixel 230 c includes a third light-emitting element 232 cprovided over the substrate 100 and a third color filter layer 134 cprovided for the counter substrate 128 in a region overlapping with thethird light-emitting element 232 c.

In the display device illustrated in FIG. 2A, the first color filterlayer 134 a, the second color filter layer 134 b, and the third colorfilter layer 134 c transmit light with different wavelengths. In thisembodiment, the case where the central wavelength of the wavelengthrange of light passing through the first color filter layer 134 a (λ1)is longer than the central wavelength of the wavelength range of lightpassing through the second color filter layer 134 b (λ2), and thecentral wavelength of the wavelength range of light passing through thesecond color filter layer 134 b (λ2) is longer than the centralwavelength of the wavelength range of light passing through the thirdcolor filter layer 134 c (hereinafter, also referred to as λ3) will bedescribed as an example.

For example, when the first color filter layer 134 a is red, the secondcolor filter layer 134 b is green, and the third color filter layer 134c is blue, a display device capable of full-color display can beobtained.

The first light-emitting element 232 a includes the first electrode 102a having a reflective property, and the first conductive layer 104 ahaving a light-transmitting property, the first EL layer 106, the chargegeneration layer 108, a second EL layer 210, and the electrode 112having a light-transmitting property which are stacked in this orderover the first electrode 102 a having a reflective property. The secondlight-emitting element 232 b includes the second electrode 102 b havinga reflective property, and the second conductive layer 104 b having alight-transmitting property, the first EL layer 106, the chargegeneration layer 108, the second EL layer 210, and the electrode 112having a light-transmitting property which are stacked in this orderover the second electrode 102 b having a reflective property. The thirdlight-emitting element 232 c includes a third electrode 102 c having areflective property, and a third conductive layer 104 c having alight-transmitting property, the first EL layer 106, the chargegeneration layer 108, the second EL layer 210, and the electrode 112having a light-transmitting property which are stacked in this orderover the third electrode 102 c having a reflective property.

In FIGS. 2A, 2B1, 2B2, and 2B3, light emitted from the firstlight-emitting element 232 a, the second light-emitting element 232 b,and the third light-emitting element 232 c is extracted from theelectrode 112 side. The first light-emitting element 232 a, the secondlight-emitting element 232 b, and the third light-emitting element 232 care electrically insulated from each other by the insulating layer 126.

FIG. 2B1 is an enlarged view of the first light-emitting element 232 a.FIG. 2B2 is an enlarged view of the second light-emitting element 232 b.FIG. 2B3 is an enlarged view of the third light-emitting element 232 c.

The first light-emitting element 232 a, the second light-emittingelement 232 b, and the third light-emitting element 232 c are differentfrom the first light-emitting element 132 a and the secondlight-emitting element 132 b illustrated in FIGS. 1A, 1B1, and 1B2 inthe structure of the second EL layer provided over the charge generationlayer 108. The first light-emitting element 232 a, the secondlight-emitting element 232 b, and the third light-emitting element 232 ceach include the second EL layer 210 including at least the secondlight-emitting layer 122 and a third light-emitting layer 124. Note thatthe second EL layer 210 can have a stacked-layer structure includingfunctional layers such as a hole-injection layer, a hole-transportlayer, an electron-transport layer, and an electron-injection layer, inaddition to the light-emitting layer. Other structures are similar tothe structure of the first light-emitting element 132 a or the secondlight-emitting element 132 b.

The first light-emitting element 232 a, the second light-emittingelement 232 b, and the third light-emitting element 232 c respectivelyinclude the first conductive layer 104 a having a light-transmittingproperty, the second conductive layer 104 b having a light-transmittingproperty, and the third conductive layer 104 c having alight-transmitting property which have different thicknesses; therefore,the total thicknesses of the first light-emitting element 232 a, thesecond light-emitting element 232 b, and the third light-emittingelement 232 c are different from one another.

The third conductive layer 104 c having a light-transmitting propertyhas a function of adjusting the optical path length of light which isemitted from the third light-emitting layer 124 and reflected back bythe third reflected electrode 102 c (the light is also referred to asthird reflected light) by adjusting the thickness of the thirdconductive layer 104 c having a light-transmitting property. The thirdreflected light interferes with light entering the third color filterlayer 134 c directly from the third light-emitting layer 124 (the lightis also referred to as third entering light). Thus, the phases of thethird entering light and the third reflected light are aligned byadjusting the thickness of the third conductive layer 104 c having alight-transmitting property, whereby light emitted from the thirdlight-emitting layer 124 can be amplified. Thus, the luminance of thelight-emitting element according to this embodiment is higher than theluminance of a light-emitting element in which the optical path lengthis not adjusted, in the case where the same current is applied to theselight-emitting elements. In addition, the phases of the third enteringlight and the third reflected light are aligned with the centralwavelength of the light passing through the third color filter layer 134c, whereby the color purity of light extracted from the third pixel 230c can be improved.

Specifically, it is preferable that the optical path length between thefirst electrode 102 a having a reflective property and the firstlight-emitting layer 120 in the first light-emitting element 232 aincluded in the first pixel 230 a be one-quarter of the centralwavelength of the wavelength range of light passing through the firstcolor filter layer 134 a (λ1). Moreover, it is preferable that theoptical path length between the second electrode 102 b having areflective property and the second light-emitting layer 122 in thesecond light-emitting element 232 b included in the second pixel 230 bbe three-quarters of the central wavelength of the wavelength range oflight passing through the second color filter layer 134 b (λ2).Furthermore, it is preferable that the optical path length between thethird electrode 102 c having a reflective property and the thirdlight-emitting layer 124 in the third light-emitting element 232 cincluded in the third pixel 230 c be five-quarters of the centralwavelength of the wavelength range of light passing through the thirdcolor filter layer 134 c (λ3).

The central wavelength of the wavelength range of light passing throughthe first color filter layer 134 a and the peak of the spectrum of lightemitted from the first light-emitting layer 120 are preferably in thewavelength region exhibiting the same color. The central wavelength ofthe wavelength range of light passing through the second color filterlayer 134 b and the peak of the spectrum of light emitted from thesecond light-emitting layer 122 are preferably in the wavelength regionexhibiting the same color. Moreover, the central wavelength of thewavelength range of light passing through the third color filter layer134 c and the peak of the spectrum of light emitted from the thirdlight-emitting layer 124 are preferably in the wavelength regionexhibiting the same color.

For example, in the case where the first color filter layer 134 a has acentral wavelength in the red region (e.g., the case where the centralwavelength is 690 nm), the spectrum of light emitted from the firstlight-emitting layer 120 preferably has a peak in the range of 600 nm to700 nm. For example, in the case where the second color filter layer 134b has a central wavelength in the green region (e.g., the case where thecentral wavelength is 550 nm), the spectrum of light emitted from thesecond light-emitting layer 122 preferably has a peak in the range of520 nm to 550 nm. For example, in the case where the third color filterlayer 134 c has a central wavelength in the blue region (e.g., the casewhere the central wavelength is 450 nm), the spectrum of light emittedfrom the third light-emitting layer 124 preferably has a peak in therange of 430 nm to 470 nm.

Note that in this embodiment, the central wavelength of the wavelengthrange of light passing through the first color filter layer 134 a islonger than the central wavelength of the wavelength range of lightpassing through the second color filter layer 134 b, and the centralwavelength of the wavelength range of light passing through the secondcolor filter layer 134 b is longer than the central wavelength of thewavelength range of light passing through the third color filter layer134 c; therefore, it is preferable that the wavelength of a color oflight emitted from the first light-emitting layer 120 be longer than thewavelength of a color of light emitted from the second light-emittinglayer 122 and that the wavelength of the color of light emitted from thesecond light-emitting layer 122 be longer than the wavelength of a colorof light emitted from the third light-emitting layer 124.

The second EL layer 210 include at least the second light-emitting layer122 and the third light-emitting layer 124 stacked over the secondlight-emitting layer 122. The description of the second EL layer 110 maybe referred to for the specific structure of the second EL layer 210.Note that a light-emitting material which emits light with a wavelengthshorter than the wavelength of a color of light emitted from the secondlight-emitting layer 122 is used as a light-emitting material of thethird light-emitting layer 124.

FIG. 3 is a plan view of a structure of an electrode of a displayportion in the display device of this embodiment. Note that somecomponents (e.g., the second EL layer) are omitted in FIG. 3 for easyunderstanding. The display device in FIG. 3 is a passive matrix displaydevice. In the display device, the electrodes 102 having reflectiveproperties processed in stripes (a first electrode 102 a having areflective property, a second electrode 102 b having a reflectiveproperty, and a third electrode 102 c having a reflective property) andthe electrodes 112 having light-transmitting properties processed instripes (a first electrode 112 a having a light-transmitting property, asecond electrode 112 b having a light-transmitting property, and a thirdelectrode 112 c having a light-transmitting property) are stacked tofoul a lattice.

The first EL layer, the charge generation layer, and the second EL layerare each formed as a continuous film over an entire area between anelectrode 102 having a reflective property and the electrode 112 havinga light-transmitting property. Thus, selective deposition using a metalmask is not needed.

In the display device described in this embodiment, the optical pathlength between the electrode having a reflective property and thelight-emitting layer is optimized in accordance with the color filterlayer exhibiting a color of a pixel, whereby light of each color can beextracted from the pixel with high color purity and high emissionefficiency. The light-emitting layer is formed as a continuous filmwithout performing selective deposition of light-emitting layers inpixels with the use of a metal mask. This can prevent a reduction inyield or a complicated process caused by the use of a metal mask. Thus,a high-definition and low-power-consumption display device can beprovided.

The structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

(Embodiment 2)

In this embodiment, an active matrix display device that is oneembodiment of the present invention will be described with reference toFIGS. 4A and 4B. FIG. 4A is a plan view illustrating a display device.FIG. 4B is a cross-sectional view taken along line A-B and C-D in FIG.4A

In the display device illustrated in FIGS. 4A and 4B, an elementsubstrate 410 and a sealing substrate 404 are attached to each otherwith a sealant 405, and a driver circuit portion (a source-side drivercircuit 401 and a gate side driver circuit 403) and a pixel portion 402including a plurality of pixels are provided.

Note that a wiring 408 is a wiring for transmitting signals that are tobe inputted to the source side driver circuit 401 and the gate sidedriver circuit 403, and receives a video signal, a clock signal, a startsignal, a reset signal, and the like from a flexible printed circuit(FPC) 409 which serves as an external input terminal. Although only theFPC is illustrated here, a printed wiring board (PWB) may be attached tothe FPC. The display device in this specification includes not only adisplay device itself but also a display device to which an FPC or a PWBis attached.

The driver circuit portion (the source side driver circuit 401 and thegate side driver circuit 403) includes a plurality of transistors. Aplurality of pixels included in the pixel portion 402 each include aswitching transistor, a current controlling transistor, and a firstelectrode electrically connected to a drain electrode of the currentcontrolling transistor.

Although the driver circuit portion (the source side driver circuit 401and the gate side driver circuit 403) and the pixel portion 402 areformed over the element substrate 410, FIG. 4B illustrates the sourceside driver circuit 401 which is the driver circuit portion and threepixels in the pixel portion 402.

The plurality of pixels in the pixel portion 402 each include theswitching transistor, the current controlling transistor, and the firstelectrode electrically connected to a drain electrode of the currentcontrolling transistor. The plurality of pixels include at least twopixels. In this embodiment, an example is described in which pixels ofthree colors, a red (R) pixel 420 a, a green (G) pixel 420 b, and a blue(B) pixel 420 c, are provided.

The pixels 420 a, 420 b, and 420 c respectively include color filterlayers 434 a, 434 b, 434 c; light-emitting elements 418 a, 418 b, and418 c; and transistors 412 a, 412 b, and 412 c which are respectivelyelectrically connected to the light-emitting elements 418 a, 418 b, and418 c and function as switching transistors.

The light-emitting elements 418 a, 418 b, and 418 c respectively includea stacked layer of an electrode 413 a having a reflective property and aconductive layer 415 a having a light-transmitting property, a stackedlayer of an electrode 413 b having a reflective property and aconductive layer 415 b having a light-transmitting property, and astacked layer of an electrode 413 c having a reflective property and aconductive layer 415 c having a light-transmitting property. Inaddition, the light-emitting elements 418 a, 418 b, and 418 c include,over the respective stacked layers, a first EL layer 431 in which afirst light-emitting layer is provided, a charge generation layer 432,and a second EL layer 433 in which a second light-emitting layer and athird light-emitting layer are provided, and an electrode 417 having alight-transmitting property.

By adjusting the thickness of the conductive layer 415 a having alight-transmitting property, the optical path length between theelectrode 413 a having a reflective property and the firstlight-emitting layer in the red (R) pixel 420 a is set to one-quarter ofthe central wavelength of the wavelength range of light passing throughthe color filter layer 434 a. By adjusting the thickness of theconductive layer 415 b having a light-transmitting property, the opticalpath length between the electrode 413 b having a reflective property andthe second light-emitting layer in the green (G) pixel 420 b is set tothree-quarters of the central wavelength of the wavelength range oflight passing through the color filter layer 434 b. By adjusting thethickness of the conductive layer 415 c having a light-transmittingproperty, the optical path length between the electrode 413 c having areflective property and the third light-emitting layer in the blue (B)pixel 420 c is set to five-quarters of the central wavelength of thewavelength range of light passing through the color filter layer 434 c.

For example, the color filter layer 434 a of the red (R) pixel 420 a maybe red with a central wavelength of 690 nm, the color filter layer 434 bof the green (G) pixel 420 b may be green with a central wavelength of550 nm, and the color filter layer 434 c of the blue (B) pixel 420 c maybe blue with a central wavelength of 450 nm.

The optical path length between the electrode having a reflectiveproperty and the light-emitting layer is optimized in accordance withthe color filter layer exhibiting a color of a pixel, light of eachcolor can be extracted from each pixel with high color purity and highemission efficiency. The light-emitting layer is formed as a continuousfilm without performing selective deposition of light-emitting layers inpixels with the use of a metal mask. This can prevent a reduction inyield or a complicated process caused by the use of a metal mask. Thus,a high-definition display device with excellent color reproducibilitycan be provided. Moreover, a low-power-consumption display device can beprovided.

A CMOS circuit, which is a combination of an n-channel transistor 423and a p-channel transistor 424, is formed for the source side drivercircuit 401. The driver circuit may be any of a variety of circuitsformed with transistors, such as a CMOS circuit, a PMOS circuit, or anNMOS circuit. Although the example in which the source side drivercircuit and the gate side driver circuit are formed over a substrate isdescribed in this embodiment, one embodiment of the present invention isnot limited thereto. All or part of the source side driver circuit andthe gate side driver circuit may be formed outside a substrate, not overthe substrate.

Note that an insulator 414 is formed to cover end portions of theelectrodes 413 a, 413 b, and 413 c having reflective properties and endportions of the conductive layers 415 a, 415 b, and 415 c havinglight-transmitting properties. Here, the insulator 414 is formed using apositive type photosensitive acrylic resin film.

In order to improve the coverage, the insulator 414 is provided suchthat either an upper end portion or a lower end portion of the insulator414 has a curved surface with a curvature. For example, when positivephotosensitive acrylic is used as a material for the insulator 414, itis preferable that only an upper end portion of the insulator 414 have acurved surface with a radius of curvature (0.2 μm to 3 μm). For theinsulator 414, it is also possible to use either a negative typephotosensitive material that becomes insoluble in an etchant by lightirradiation or a positive type photosensitive material that becomessoluble in an etchant by light irradiation.

Any of the materials described in Embodiment 1 can be used for each ofthe color filter layers 434 a, 434 b, and 434 c, the electrodes 413 a,413 b, and 413 c having reflective properties, the conductive layers 415a, 415 b, and 415 c having light-transmitting properties, the first ELlayer 431, the charge generation layer 432, the second EL layer 433, andthe electrode 417 having a light-transmitting property.

The sealing substrate 404 is attached to the element substrate 410 withthe sealant 405; thus, a light-emitting element 418 is provided in aspace 407 enclosed by the element substrate 410, the sealing substrate404, and the sealant 405. Note that the space 407 is filled with afiller and may be filled with an inert gas (e.g., nitrogen or argon), anorganic resin, or the sealant 405. A substance having a hygroscopicproperty may be used as the organic resin and the sealant 405.

Note that an epoxy-based resin is preferably used as the sealant 405. Itis preferable that such a material allow as little moisture and oxygenas possible to penetrate. As a material for the sealing substrate 404, aglass substrate, a quartz substrate, or a plastic substrate made offiberglass-reinforced plastics (FRP), polyvinyl fluoride (PVF),polyester, acrylic, or the like can be used.

As in this embodiment, an insulating film 411 which serves as a basefilm may be provided between the element substrate 410 and asemiconductor layer of the transistor. The insulating film has afunction of preventing diffusion of an impurity element from the elementsubstrate 410 and can be formed to have a single-layer structure or astacked-layer structure using one or more of a silicon nitride film, asilicon oxide film, a silicon nitride oxide film, and a siliconoxynitride film.

There is no particular limitation on the structure of the transistorwhich can be used in the display device disclosed in this specification;for example, a staggered type transistor or a planar type transistorhaving a top-gate structure or a bottom-gate structure can be used. Thetransistor may have a single-gate structure in which one channelformation region is formed, a double-gate structure in which two channelformation regions are formed, or a triple-gate structure in which threechannel formation regions are formed. Alternatively, the transistor mayhave a dual-gate structure including two gate electrode layerspositioned over and below a channel region with gate insulating layerstherebetween.

The gate electrode layers can be formed to have a single-layer orstacked-layer structure using a metal material such as molybdenum,titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, orscandium, or an alloy material containing any of these materials as itsmain component.

For example, as a two-layer structure of the gate electrode layer, thefollowing structures are preferable: a two-layer structure of analuminum layer and a molybdenum layer stacked thereover, a two-layerstructure of a copper layer and a molybdenum layer stacked thereover, atwo-layer structure of a copper layer and a titanium nitride layer or atantalum nitride layer stacked thereover, and a two-layer structure of atitanium nitride layer and a molybdenum layer. As a three-layerstructure, a three-layer structure in which a tungsten layer or atungsten nitride layer, an alloy of aluminum and silicon or an alloy ofaluminum and titanium, and a titanium nitride layer or a titanium layerare stacked is preferable.

The gate insulating layer can be formed to have a single-layer structureor a stacked-layer structure using a silicon oxide layer, a siliconnitride layer, a silicon oxynitride layer, and/or a silicon nitrideoxide layer by a plasma CVD method, a sputtering method, or the like.Alternatively, a silicon oxide layer formed by a CVD method using anorganosilane gas can be used as the gate insulating layer. As anorganosilane gas, a silicon-containing compound such astetraethoxysilane (TEOS) (chemical formula: Si(OC₂H₅)₄),tetramethylsilane (TMS) (chemical formula: Si(CH₃)₄),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (chemical formula:SiH(OC₂H₅)₃), or trisdimethylaminosilane (chemical formula:SiH(N(CH₃)₂)₃) can be used.

A material of the semiconductor layer is not particularly limited andmay be determined as appropriate in accordance with the characteristicsneeded for the transistors 412 a, 412 b, 412 c, 423, and 424. Examplesof materials which can be used for the semiconductor layer will begiven.

As the material of the semiconductor layer, any of the following can beused: an amorphous semiconductor manufactured by a sputtering method ora vapor-phase growth method using a semiconductor material gas typifiedby silane or germane; a polycrystalline semiconductor formed bycrystallizing the amorphous semiconductor with the use of light energyor thermal energy; and a microcrystalline semiconductor. Thesemiconductor layer can be formed by a sputtering method, an LPCVDmethod, a plasma CVD method, or the like.

A single crystal semiconductor made of silicon or silicon carbide can beused for the semiconductor layer. When a single crystal semiconductor isused for the semiconductor layer, the size of the transistor can bereduced; thus, higher resolution pixels in a display portion can beobtained. In the case where a single crystal semiconductor is used forthe semiconductor layer, an SOI substrate in which a single crystalsemiconductor layer is provided can be used. Alternatively, asemiconductor substrate such as a silicon wafer may be used.

A typical example of an amorphous semiconductor is hydrogenatedamorphous silicon, and a typical example of a crystalline semiconductoris polysilicon and the like. Examples of polysilicon (polycrystallinesilicon) include so-called high-temperature polysilicon which containspolysilicon formed at a process temperature of 800° C. or higher as itsmain component, so-called low-temperature polysilicon which containspolysilicon formed at a process temperature of 600° C. or lower as itsmain component, and polysilicon obtained by crystallizing amorphoussilicon with the use of an element that promotes crystallization.Needless to say, a microcrystalline semiconductor or a semiconductorpartly containing a crystal phase can be used as described above.

Further, an oxide semiconductor may be used. As the oxide semiconductor,the following can be used: an oxide of four metal elements such as anIn—Sn—Ga—Zn—O-based oxide semiconductor; an oxide of three metalelements such as an In—Ga—Zn—O-based oxide semiconductor, anIn—Sn—Zn—O-based oxide semiconductor, an In—Al—Zn—O-based oxidesemiconductor, a Sn—Ga—Zn—O-based oxide semiconductor, anAl—Ga—Zn—O-based oxide semiconductor, or a Sn—Al—Zn—O-based oxidesemiconductor; or an oxide of two metal elements such as anIn—Zn—O-based oxide semiconductor, a Sn—Zn—O-based oxide semiconductor,an Al—Zn—O-based oxide semiconductor, a Zn—Mg—O-based oxidesemiconductor, a Sn—Mg—O-based oxide semiconductor, an In—Mg—O-basedoxide semiconductor, or In—Ga—O-based oxide semiconductor; an In—O-basedoxide semiconductor; a Sn—O-based oxide semiconductor; or a Zn—O-basedoxide semiconductor. Further, SiO₂ may be contained in the above oxidesemiconductor. Here, for example, an In—Ga—Zn—O-based oxidesemiconductor is an oxide containing at least In, Ga, and Zn, and thecomposition ratio of the elements is not particularly limited. TheIn—Ga—Zn—O-based oxide semiconductor may contain an element other thanIn, Ga, and Zn.

A thin film expressed by a chemical formula of InMO₃(ZnO)_(m) (m>0) canbe used for the oxide semiconductor layer. Here, M represents one ormore metal elements selected from Ga, Al, Mn, and Co. For example, M canbe Ga, Ga and Al, Ga and Mn, Ga and Co, or the like.

In the case where an In—Zn—O-based material is used as the oxidesemiconductor, the atomic ratio thereof is In/Zn=0.5 to 50, preferablyIn/Zn=1 to 20, further preferably In/Zn=1.5 to 15. When the atomic ratioof Zn is in the above preferred range, the field-effect mobility of atransistor can be improved. Here, when the atomic ratio of the compoundis In:Zn:O═X:Y:Z, the relation of Z>1.5X+Y is satisfied.

As the oxide semiconductor layer, a CAAC-OS (c-axis aligned crystallineoxide semiconductor) film which is neither completely single crystal norcompletely amorphous can be used. The CAAC-OS film is an oxidesemiconductor film having a crystal-amorphous mixed structure in whichan amorphous phase includes a crystal portion and an amorphous portion.In the crystal portion included in the CAAC-OS film, c-axes are alignedin the direction parallel (including the range of −5° to 5°) to a normalvector of the surface where the CAAC-OS film is formed or a normalvector of the surface of the CAAC-OS film, a triangular or hexagonalatomic arrangement is provided when seen from the directionperpendicular to an a-b plane, and metal atoms are arranged in a layeredmanner or metal atoms and oxygen atoms are arranged in a layered mannerwhen seen from the direction perpendicular (including the range of 85°to 95°) to the c-axis. Note that the directions of the a-axes and theb-axes may vary between different crystal portions.

As examples of materials for a wiring layer serving as a sourceelectrode layer or a drain electrode layer, the following are given: anelement selected from Al, Cr, Ta, Ti, Mo, and W; an alloy containing anyof the above elements as its component; an alloy film containing acombination of any of these elements; and the like. In the case whereheat treatment is performed, a conductive film preferably has heatresistance high enough to withstand the heat treatment. Since the use ofAl alone brings disadvantages such as low heat resistance and a tendencyfor corrosion, aluminum is used in combination with a conductivematerial having heat resistance. As the conductive material having heatresistance, which is combined with Al, it is possible to use an elementselected from titanium (Ti), tantalum (Ta), tungsten (W), molybdenum(Mo), chromium (Cr), neodymium (Nd), and scandium (Sc), an alloycontaining any of these elements as its component, an alloy containing acombination of any of these elements, or a nitride containing any ofthese elements as its component.

An inorganic insulating film or an organic insulating film formed by adry method or a wet method can be used for an insulating film 419 whichcovers the transistors. For example, a silicon nitride film, a siliconoxide film, a silicon oxynitride film, an aluminum oxide film, atantalum oxide film, or a gallium oxide film which is formed by a CVDmethod, a sputtering method, or the like can be used. Alternatively, anorganic material such as polyimide, acrylic, benzocyclobutene,polyamide, or an epoxy resin can be used. Other than the above organicmaterials, a low-dielectric constant material (a low-k material), asiloxane-based resin, PSG (phosphosilicate glass), BPSG(borophosphosilicate glass), or the like can be used.

Note that the siloxane-based resin corresponds to a resin including aSi—O—Si bond formed using a siloxane-based material as a startingmaterial. The siloxane-based resin may include, as a substituent, anorganic group (e.g., an alkyl group or an aryl group) or a fluoro group.The organic group may include a fluoro group. A siloxane-based resin isapplied by a coating method and baked; thus, the insulating film 419 canbe faulted.

Note that the insulating film 419 may be formed by stacking a pluralityof insulating films formed using any of the above-described materials.For example, a structure may be employed in which an organic resin filmis stacked over an inorganic insulating film.

In the above manner, the active matrix display device including thelight-emitting element of one embodiment of the present invention can beobtained.

Note that this embodiment can be freely combined with any of the otherembodiments.

(Embodiment 3)

A display device disclosed in this specification can be applied to avariety of electronic appliances (including game machines). Examples ofelectronic devices include a television set (also referred to as atelevision or a television receiver), a monitor of a computer or thelike, a camera such as a digital camera or a digital video camera, adigital photo frame, a mobile phone handset (also referred to as amobile phone or a mobile phone device), a portable game console, aportable information terminal, an audio reproducing device, and alarge-sized game machine such as a pachinko machine.

FIG. 5A illustrates a laptop personal computer, which includes a mainbody 3001, a housing 3002, a display portion 3003, a keyboard 3004, andthe like. By applying the display device described in Embodiment 1 or 2to the display portion 3003, the laptop personal computer can have ahigh level of definition and consumes a small amount of power.

FIG. 5B illustrates a personal digital assistant (PDA), which includes adisplay portion 3023, an external interface 3025, an operation button3024, and the like in a main body 3021. The personal digital assistantalso includes a stylus 3022 as an accessory for operation. By applyingthe display device described in Embodiment 1 or 2 to the display portion3023, the personal digital assistant (PDA) can have a high level ofdefinition and consumes a small amount of power.

FIG. 5C illustrates an e-book reader, which includes two housings, ahousing 2701 and a housing 2703. The housing 2701 and the housing 2703are combined with a hinge 2711 so that the e-book reader can be openedand closed with the hinge 2711 as an axis. Such a structure enables thee-book reader to operate like a paper book.

A display portion 2705 and a display portion 2707 are incorporated inthe housing 2701 and the housing 2703, respectively. The display portion2705 and the display portion 2707 may display one image or differentimages. In the case where the display portion 2705 and the displayportion 2707 display different images, for example, text can bedisplayed on a display portion on the right side (the display portion2705 in FIG. 5C) and graphics can be displayed on a display portion onthe left side (the display portion 2707 in FIG. 5C). By applying thedisplay device described in Embodiment 1 or 2 to the display portion2705 and the display portion 2707, the e-book reader can have a highlevel of definition and consumes a small amount of power. In the casewhere a semi-transmissive display device or a reflective display deviceis used for the display portion 2705, a solar battery may be provided sothat the solar battery can generate power and a battery can be chargedfor the use in relatively bright conditions. Note that when a lithiumion battery is used as the battery, an advantage such as reduction insize can be obtained.

Further, FIG. 5C illustrates an example in which the housing 2701 isprovided with an operation portion and the like. For example, thehousing 2701 is provided with a power switch 2721, operation keys 2723,a speaker 2725, and the like. Pages can be turned with the operation key2723. Note that a keyboard, a pointing device, or the like may also beprovided on the surface of the housing, on which the display portion isprovided. Furthermore, an external connection terminal (an earphoneterminal, a USB terminal, or the like), a recording medium insertionportion, and the like may be provided on the back surface or the sidesurface of the housing. Further, the e-book reader may have a functionof an electronic dictionary.

The e-book reader may wirelessly transmit and receive data. Throughwireless communication, desired book data or the like can be purchasedand downloaded from an electronic book server.

FIG. 5D illustrates a mobile phone, which includes two housings, ahousing 2800 and a housing 2801. The housing 2801 includes a displaypanel 2802, a speaker 2803, a microphone 2804, a pointing device 2806, acamera lens 2807, an external connection terminal 2808, and the like. Inaddition, the housing 2800 includes a solar cell 2810 having a functionof charging the mobile phone, an external memory slot 2811, and thelike. Further, an antenna is incorporated in the housing 2801. Byapplying the display device described in Embodiment 1 or Embodiment 2 tothe display panel 2802, the mobile phone can have a higher level ofdefinition and consumes a smaller amount of power.

The display panel 2802 is provided with a touch panel. A plurality ofoperation keys 2805 which are displayed as images are illustrated bydashed lines in FIG. 5D. Note that a boosting circuit by which voltageoutput from the solar cell 2810 is increased to be sufficiently high foreach circuit is also included.

The display direction in the display panel 2802 is changed asappropriate depending on a usage pattern. Further, the mobile phone isprovided with the camera lens 2807 on the same surface as the displaypanel 2802; thus, it can be used as a video phone. The speaker 2803 andthe microphone 2804 can be used for videophone calls, recording andplaying sound, and the like without limitation to voice calls. Moreover,the housing 2800 and the housing 2801 developed as illustrated in FIG.5D can be slid so that one is lapped over the other; thus, the size ofthe mobile phone can be reduced, which makes the mobile phone suitablefor being carried.

The external connection terminal 2808 can be connected to an AC adapterand various types of cables such as a USB cable, and charging and datacommunication with a personal computer are possible. Moreover, a largeamount of data can be stored by inserting a storage medium into theexternal memory slot 2811 and can be moved.

Further, an infrared communication function, a television receptionfunction, or the like may be provided in addition to the abovefunctions.

FIG. 5E illustrates a digital video camera, which includes a main body3051, a display portion A 3057, an eyepiece 3053, an operation switch3054, a display portion B 3055, a battery 3056, and the like. Byapplying the display device described in Embodiment 1 or Embodiment 2 toeach of the display portion A 3057 and the display portion B 3055, thedigital video camera can have a higher level of definition and consumesa smaller amount of power.

FIG. 5F illustrates a television device in which a display portion 9603and the like are incorporated in a housing 9601. Images can be displayedon the display portion 9603. Here, the housing 9601 is supported by astand 9605. By applying the display device described in Embodiment 1 orEmbodiment 2 to the display portion 9603, the television device can havea higher level of definition and consumes a smaller amount of power.

The television device can be operated by an operation switch of thehousing 9601 or a separate remote controller. Further, the remotecontroller may be provided with a display portion for displaying dataoutput from the remote controller.

Note that the television device is provided with a receiver, a modem,and the like. With the use of the receiver, general televisionbroadcasting can be received. Moreover, when the display device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

This embodiment, can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Note that the structure described in this embodiment can be combinedwith the structure described in Embodiment 1 or 2 as appropriate.

EXAMPLE

In this example, measurement results of characteristics of a displaydevice according to one embodiment of the present invention will bedescribed with reference to drawings and tables.

A manufacturing method of a light-emitting element used in a displaydevice in this example will be described with reference to FIG. 6. Thedisplay device of this example includes at least a light-emittingelement corresponding to a green pixel (hereinafter, light-emittingelement G) and a light-emitting element corresponding to a blue pixel(hereinafter, light-emitting element B).

Shown below are structural formulae of organic compounds used in thisexample (BPhen, 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: PCzPA), 9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene(abbreviation: CzPA), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP),N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn),2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBA1BP),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₂(acac)), andbis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III)(abbreviation: Ir(tppr)₂(dpm))).

As an electrode 1101 having a reflective property of each of thelight-emitting element G and the light-emitting element B, analuminum-titanium alloy film was formed over a substrate 1100 which wasa glass substrate by a sputtering method. In this example, the electrode1101 having a reflective property was used as an anode.

Next, titanium (Ti) and then indium tin oxide containing silicon oxide(ITSO) were deposited over the electrode 1101 having a reflectiveproperty by a sputtering method to form a conductive layer 1104 having alight-transmitting property. Note that the deposited Ti was oxidized tobe titanium oxide (TiOx) after the sputtering of ITSO, and thus had alight-transmitting property. Then, ITSO was removed by etching in thelight-emitting element B.

By the above method, a stacked layer of TiOx with a thickness of 6 nmand ITSO with a thickness of 40 nm was employed as the conductive layer1104 having a light-transmitting property in the light-emitting elementCr, and TiOx with a thickness of 6 nm was employed as the conductivelayer 1104 having a light-transmitting property in the light-emittingelement B in order to obtain a cavity effect in each of a pixelincluding the light-emitting element B (hereinafter, pixel B) and apixel including the light-emitting element G (hereinafter, pixel G) inthis example. Then, the periphery of the conductive layer 1104 having alight-transmitting property was covered with a polyimide film such thatan area of 2 mm×2 mm of the surface was exposed, which corresponded tothe electrode area.

Next, the substrate 1100 provided with the electrode 1101 having areflective property and the conductive layer 1104 having alight-transmitting property was fixed to a substrate holder provided ina vacuum evaporation apparatus such that the surface on which theelectrode 1101 having a reflective property and the conductive layer1104 having a light-transmitting property were formed faced downward,and then the pressure was reduced to about 10⁻⁴ Pa. After that, PCzPAand molybdenum(VI) oxide were co-evaporated on the conductive layer 1104having a light-transmitting property to form a hole-injection layer1111. The weight ratio of PCzPA to molybdenum oxide was adjusted to be1:0.5 (=PCzPA: molybdenum oxide). The thickness of the hole-injectionlayer 1111 was 5 nm. Note that the co-evaporation method refers to anevaporation method in which evaporation is carried out from a pluralityof evaporation sources at the same time in one treatment chamber.

Next, BPAFLP was deposited to a thickness of 10 nm on the hole-injectionlayer 1111 to form a hole-transport layer 1112.

On the hole-transport layer 1112, 2mDBTPDBq-II, PCBA1BP, andIr(tBuppm)₂(acac) were co-evaporated so that the weight ratio of2mDBTPDBq-II to PCBA1BP and Ir(tBuppm)₂(acac) was 0.8:0.2:0.06 to form alight-emitting layer 1113. The thickness of the light-emitting layer1113 was 20 nm.

On the light-emitting layer 1113, 2mDBTPDBq-II and Ir(tppr)₂(dpm) wereco-evaporated so that the weight ratio of 2mDBTPDBq-II to Ir(tppr)₂(dpm)was 1:0.06 to form a light-emitting layer 1213. The thickness of thelight-emitting layer 1213 was 20 nm.

On the light-emitting layer 1213, 2mDBTPDBq-LE was deposited to athickness of 15 nm to form an electron-transport layer 1114 a.

On the electron-transport layer 1114 a, bathophenanthroline(abbreviation: BPhen) was deposited to a thickness of 15 nm to form anelectron-transport layer 1114 b.

On the electron-transport layer 1114 b, lithium oxide (Li₂O) wasevaporated to a thickness of 0.1 nm to form an electron-injection layer1115 a, and on the electron-injection layer 1115 a, copper(II)phthalocyanine (abbreviation: CuPc) was evaporated to a thickness of 2nm to form an electron-injection layer 1115 b.

On the electron-injection layer 1115 b, PCzPA and molybdenum(VI) oxidewere co-evaporated to form a charge generation layer 1102. The weightratio of PCzPA to molybdenum oxide was adjusted to be 1:0.5 (=PCzPA:molybdenum oxide). The thickness of the charge generation layer 1102 was55 nm.

On the charge generation layer 1102, PCzPA was deposited to a thicknessof 20 nm to form a hole-transport layer 1212.

On the hole-transport layer 1212, CzPA and 1,6mMemFLPAPrn wereco-evaporated so that the weight ratio of CzPA to 1,6mMemFLPAPrn was1:0.05 to form a light-emitting layer 1313. The thickness of thelight-emitting layer 1313 was 30 nm.

On the light-emitting layer 1313, CzPA was deposited to a thickness of 5nm to form an electron-transport layer 1214 a.

On the electron-transport layer 1214 a, BPhen was deposited to athickness of 15 nm to form an electron-transport layer 1214 b.

On the electron-transport layer 1214 b, lithium fluoride (LiF) wasdeposited to a thickness of 1 nm to form an electron-injection layer1215.

On the electron-injection layer 1215, silver and magnesium weredeposited to a thickness of 15 nm so that the volume ratio of silver tomagnesium was 10:1 to form a film containing silver and magnesium (AgMgfilm) as a conductive layer 1105.

On the conductive layer 1105, indium tin oxide (ITO) was deposited to athickness of 70 nm by a sputtering method to form an electrode 1103having a light-transmitting property.

Through the above steps, the light-emitting element G and thelight-emitting element B which were used in this example weremanufactured.

Note that in all of the above evaporation steps, a resistance heatingmethod was employed.

Table 1 shows the element structures of the light-emitting element G andthe light-emitting element B which were manufactured in the abovemanner.

TABLE 1 1101 1104 1111 1112 1113 light-emitting Al—Ti TiOx\ITSOPCzPA:MoOx BPAFLP 2mDBTPDBq-II:PCBA1BP:Ir(tBuppm)₂(acac) element G 6nm\40 nm (=1:0.5) 10 nm (=0.8:0.2:0.06) 5 nm 20 nm light-emitting Al—TiTiOx PCzPA:MoOx BPAFLP 2mDBTPDBq-II:PCBA1BP:Ir(tBuppm)₂(acac) element B6 nm (=1:0.5) 10 nm (=0.8:0.2:0.06) 5 nm 20 nm 1213 1114a 1114b 1115a1115b 1102 1212 light-emitting 2mDBTPDBq-II:Ir(tppr)₂(dpm) 2mDBTPDBq-IIBPhen Li₂O CuPc PCzPA:MoOx PCzPA element G (=1:0.06) 15 nm 15 nm 0.1 nm2 nm (=1:0.5) 20 nm 20 nm 55 nm light-emitting2mDBTPDBq-II:Ir(tppr)₂(dpm) 2mDBTPDBq-II BPhen Li₂O CuPc PCzPA:MoOxPCzPA element B (=1:0.06) 15 nm 15 nm 0.1 nm 2 nm (=1:0.5) 20 nm 20 nm55 nm 1313 1214a 1214b 1215 1105 1103 light-emitting CzPA:1,6- CzPABPhen LiF Ag:Mg ITO element G mMemFLPAPrn 5 nm 15 nm 1 nm (=10:1) 70 nm(=1:0.05) 15 nm 30 nm light-emitting CzPA:1,6- CzPA BPhen LiF Ag:Mg ITOelement B mMemFLPAPrn 5 nm 15 nm 1 nm (=10:1) 70 nm (=1:0.05) 15 nm 30nm

The light-emitting element G and the light-emitting element B weresealed with a glass substrate in a glove box under a nitrogen atmosphereso as not to be exposed to the air.

Then, the light-emitting element G and a color filter layer CF (G)overlap to form the pixel G, and the light-emitting element B and acolor filter layer CF (B) overlap to form the pixel B.

The color filter layer CF (G) and the color filter layer CF (B) wereeach formed in such a manner that CB-7001W (manufactured by FUJIFILMCorporation) which was used as a material was applied onto a glasssubstrate, and then baked at 220° C. for an hour. Note that thethickness was 1.3 μm to 1.4 μm. Note that the color filter material wasapplied onto the glass substrate by a spin coating method at a spinningrate of 1000 rpm for the color filter layer CF (G) and at a spinningrate of 2000 rpm for the color filter layer CF (B).

FIG. 7 shows the relation between wavelength and transmittance of thecolor filter layer CF (G) and the color filter layer CF (B). In FIG. 7,the thin dashed line represents the color filter layer CF (G) and thethick dashed line represents the color filter layer CF (B). Thetransmittance was measured with U-4000 Spectrophotometer (manufacturedby Hitachi High-Technologies Corporation.) by setting light emitted froma light source and passing through the glass substrate to 100%.

FIG. 7 shows that the wavelength range in which the color filter layerCF (G) has a transmittance of 50% or higher in the visible light range(380 nm to 680 nm) is 511 nm to 584 nm and the central wavelength is 548nm. Moreover, the wavelength range in which the color filter layer CF(B) has a transmittance of 50% or higher in the visible light range (380nm to 680 nm) is 410 nm to 516 nm and the central wavelength is 463 nm.

In the pixel G described in this example, the optical path lengthbetween the electrode 1101 having a reflective property and thelight-emitting layer 1113 was set to one-quarter of the centralwavelength of light passing through the color filter layer CF (B) byadjusting the thickness of the conductive layer 1104 having alight-transmitting property of the light-emitting element G. Note thatthe optical path length is calculated by the following formula:refractive index×length (thickness). Table 2 shows the thickness andrefractive index at a wavelength of about 548 nm of each layer, whichwere used for calculating the optical path length of the light-emittingelement G, and the calculated optical path lengths.

TABLE 2 Thickness Refractive index Optical path (nm) at about 548 nmlength (nm) TiOx 6 2.48 14.88 ITSO 40 2.13 85.2 CzPA-OMOx 5 1.8 9 BPAFLP10 1.75 17.5 Total 126.58 ¼ of central wavelength (548 nm) of light 137passing through CF (G) Refractive index of light-emitting layer 1.8 1113(2mDBTPDBq-II) Light-emitting region (distance from interface 6 betweenhole-transport layer 1112 and light- emitting layer 1113 tolight-emitting region)

Table 2 shows that in the light-emitting element G, the optical pathlength between a light-emitting region of the light-emitting layer 1113at about 6 nm from an interface with the hole-injection layer 1111 andthe electrode 1101 having a reflective property corresponds toone-quarter of the central wavelength (548 nm) of light passing throughthe color filter, layer CF (G).

Further, in the pixel B, the optical path length between the electrode1101 having a reflective property and the light-emitting layer 1313 wasset to three-quarters of the central wavelength of light passing throughthe color filter layer CF (B). Table 3 shows the thickness andrefractive index at a wavelength of about 463 nm of each layer, whichwere used for calculating the optical path length of the light-emittingelement B, and the calculated optical path lengths.

TABLE 3 Thickness Refractive index Optical path (nm) at about 463 nmlength (nm) TiOx 6 2.56 15.36 ITSO 0 2.18 0 CzPA-OMOx 5 1.86 9.3 BPAFLP10 1.79 17.9 Light-emitting layer 1113 20 1.86 37.2 (2mDBTPDBq-II)Light-emitting layer 1213 20 1.86 37.2 (2mDBTPDBq-II) 2mDBTPDBq-II 151.86 27.9 BPhen 15 1.75 26.25 CuPc 2 1.49 2.98 PCzPA-OMOx 55 1.91 105.05PCzPA 20 1.92 38.4 Total 317.54 ¾ of central wavelength (463 nm) oflight 347.25 passing through CF (B) Refractive index of light-emittinglayer 1313 (CzPA) 1.86 Light-emitting region (distance from interface 16between hole-transport layer 1212 and light-emitting layer 1313 tolight-emitting region)

Table 3 shows that in the light-emitting element B, the optical pathlength between a light-emitting region of the light-emitting layer 1313at about 16 nm from an interface with the hole-transport layer 1212 andthe electrode 1101 having a reflective property corresponds tothree-quarters of the central wavelength (463 nm) of light passingthrough the color filter layer CF (B).

The current efficiency, the CIE chromaticity coordinates (x, y), and thevoltage of each of the pixel G and the pixel B were measured under thecondition in which a luminance of about 1000 cd/m² was able to beobtained. Note that the measurement was carried out at room temperature(in the atmosphere kept at 25° C.).

As for the pixel G, the current efficiency was 24 cd/A, the CIEchromaticity coordinates were (x, y)=(0.29, 0.68), and the voltage was6.1 V. As for the pixel B, the current efficiency was 2.3 cd/A, the CMchromaticity coordinates were (x, y)=(0.14, 0.09), and the voltage was7.9 V.

The chromaticities of the pixel G and the pixel B are shown in thechromaticity coordinates in FIG. 8. In FIG. 8, the triangle dotcorresponds to the pixel G, the square dot corresponds to the pixel B,and the solid line represents the NTSC ratio defined by NTSC.

FIG. 8 shows that both the pixel G and the pixel B have less deviationfrom the NTSC ratio, and thus are pixels with high color purity.

The above confirmed that the application of one embodiment of thepresent invention makes it possible to provide a display device withhigh color reproducibility which has pixels with high color purity.

EXPLANATION OF REFERENCE

-   100: substrate, 102: electrode, 102 a: electrode, 102 b: electrode,    102 c: electrode, 104 a: conductive layer, 104 b: conductive layer,    104 c: conductive layer, 106: EL layer, 108: charge generation    layer, 110: EL layer, 112: electrode, 112 a: electrode, 112 b:    electrode, 112 c: electrode, 120: light-emitting layer, 122:    light-emitting layer, 124: light-emitting layer, 126: insulating    layer, 128: counter substrate, 130 a: pixel, 130 b: pixel, 132 a:    light-emitting element, 132 b: light-emitting element, 134 a: color    filter layer, 134 b: color filter layer, 134 c: color filter layer,    210: EL layer, 230 a: pixel, 230 b: pixel, 230 c: pixel, 232 a:    light-emitting element, 232 b: light-emitting element, 232 c:    light-emitting element, 401: source side driver circuit, 402: pixel    portion, 403: gate side driver circuit, 404: sealing substrate, 405:    sealant, 407: space, 408: wiring, 410: element substrate, 411:    insulating film, 412 a: transistor, 412 b: transistor, 412 c:    transistor, 413 a: electrode, 413 b: electrode, 413 c: electrode,    414: insulator, 415 a: conductive layer, 415 b: conductive layer,    415 c: conductive layer, 417: electrode, 418: light-emitting    element, 418 a: light-emitting element, 418 b: light-emitting    element, 418 c: light-emitting element, 419: insulating film, 420 a:    pixel, 420 b: pixel, 420 c: pixel, 423: n-channel transistor, 424:    p-channel transistor, 431: EL layer, 432: charge generation layer,    433: EL layer, 434 a: color filter layer, 434 b: color filter layer,    434 c: color filter layer, 2701: housing, 2703: housing, 2705:    display portion, 2707: display portion, 2711: hinge, 2721: power    switch, 2723: operation key, 2725: speaker, 2800: housing, 2801:    housing, 2802: display panel, 2803: speaker, 2804: microphone, 2805:    operation key, 2806: pointing device, 2807: camera lens, 2808:    external connection terminal, 2810: solar cell, 2811: external    memory slot, 3001: main body, 3002: housing, 3003: display portion,    3004: keyboard, 3021: main body, 3022: stylus, 3023: display    portion, 3024: operation button, 3025: external interface, 3051:    main body, 3053: eyepiece, 3054: operation switch, 3056: battery,    9601: housing, 9603: display portion, and 9605: stand.

This application is based on Japanese Patent Application serial no.2011-027961 filed with Japan Patent Office on Feb. 11, 2011, the entirecontents of which are hereby incorporated by reference.

The invention claimed is:
 1. A light-emitting device comprising: a firstelement comprising: a first color filter layer; and a firstlight-emitting element, wherein the first light-emitting elementcomprises: a first electrode having a reflective property; a firstlight-emitting layer over the first electrode; and a secondlight-emitting layer over the first light-emitting layer; and a secondelement comprising: a second color filter layer; and a secondlight-emitting element, wherein the second light-emitting elementcomprises: a second electrode having a reflective property; the firstlight-emitting layer over the second electrode; and the secondlight-emitting layer over the first light-emitting layer, wherein afirst optical path length is an optical path length between the firstelectrode and the first light-emitting layer, and the first optical pathlength is determined based on a first wavelength range in which thefirst color filter layer has a transmittance of 50% or higher in thevisible light range, wherein a second optical path length is an opticalpath length between the second electrode and the second light-emittinglayer, and the second optical path length is determined based on asecond wavelength range in which the second color filter layer has atransmittance of 50% or higher in the visible light range, and wherein awavelength of a color of light emitted from the first light-emittinglayer is longer than a wavelength of a color of light emitted from thesecond light-emitting layer.
 2. The light-emitting device according toclaim 1, wherein the first optical path length is one-quarter of a firstcentral wavelength of the first wavelength range, wherein the secondoptical path length is three-quarters of a second central wavelength ofthe second wavelength range, and wherein the first central wavelength islonger than the second central wavelength.
 3. The light-emitting deviceaccording to claim 1, wherein the second light-emitting element furthercomprises a first conductive layer having a light-transmitting propertybetween the second electrode and the first light-emitting layer.
 4. Thelight-emitting device according to claim 3, wherein the first conductivelayer comprises a material selected from a group consisting of indiumoxide, indium tin oxide, an indium oxide-zinc oxide alloy, zinc oxide,zinc oxide to which gallium is added, graphene, polyaniline or aderivative thereof, polypyrrole or a derivative thereof, polythiopheneor a derivative thereof, and a copolymer of two or more of aniline,pyrrole, and thiophene or a derivative thereof.
 5. The light-emittingdevice according to claim 3, wherein the first light-emitting elementfurther comprises a second conductive layer having a light-transmittingproperty between the first electrode and the first light-emitting layer,and wherein the second conductive layer has a different thickness fromthe first conductive layer.
 6. The light-emitting device according toclaim 5, wherein the second conductive layer comprises a materialselected from a group consisting of indium oxide, indium tin oxide, anindium oxide-zinc oxide alloy, zinc oxide, zinc oxide to which galliumis added, graphene, polyaniline or a derivative thereof, polypyrrole ora derivative thereof, polythiophene or a derivative thereof, and acopolymer of two or more of aniline, pyrrole, and thiophene or aderivative thereof.
 7. The light-emitting device according to claim 1,further comprising a charge generation layer between the firstlight-emitting layer and the second light-emitting layer.
 8. Thelight-emitting device according to claim 1, further comprising anelectrode having a light-transmitting property over the secondlight-emitting layer.
 9. The light-emitting device according to claim 1,wherein the first optical path length is an optical path length betweena surface of the first electrode and a lower surface of the firstlight-emitting layer or more and an optical path length between thesurface of the first electrode and an upper surface of the firstlight-emitting layer or less, and wherein the second optical path lengthis an optical path length between a surface of the second electrode anda lower surface of the second light-emitting layer or more and anoptical path length between the surface of the second electrode and anupper surface of the second light-emitting layer or less.
 10. Thelight-emitting device according to claim 1, wherein the light-emittingdevice is a display device.
 11. A light-emitting device comprising: afirst element comprising: a first color filter layer; and a firstlight-emitting element, wherein the first light-emitting elementcomprises: a first electrode having a reflective property; a firstlight-emitting layer over the first electrode ; a second light-emittinglayer over the first light-emitting layer; and a third light-emittinglayer over the second light-emitting layer; a second element comprising:a second color filter layer; and a second light-emitting element,wherein the second light-emitting element comprises: a second electrodehaving a reflective property; the first light-emitting layer over thesecond electrode; the second light-emitting layer over the firstlight-emitting layer; and the third light-emitting layer over the secondlight-emitting layer; and a third element comprising: a third colorfilter layer; and a third light-emitting element, wherein the thirdlight-emitting element comprises: a third electrode having a reflectiveproperty; the first light-emitting layer over the third electrode; thesecond light-emitting layer over the first light-emitting layer; and thethird light-emitting layer over the second light-emitting layer, whereina first optical path length is an optical path length between the firstelectrode and the first light-emitting layer, and the first optical pathlength is determined based on a first wavelength range in which thefirst color filter layer has a transmittance of 50% or higher in thevisible light range, wherein a second optical path length is an opticalpath length between the second electrode having a reflective propertyand the second light-emitting layer in the second element, and thesecond optical path length is determined based on a second wavelengthrange in which the second color filter layer has a transmittance of 50%or higher in the visible light range, wherein a third optical pathlength is an optical path length between the third electrode having areflective property and the third light-emitting layer in the thirdelement, and the third optical path length is determined based on athird wavelength range in which the third color filter layer has atransmittance of 50% or higher in the visible light range, wherein awavelength of a color of light emitted from the first light-emittinglayer is longer than a wavelength of a color of light emitted from thesecond light-emitting layer, and wherein a wavelength of a color oflight emitted from the second light-emitting layer is longer than awavelength of a color of light emitted from the third light-emittinglayer.
 12. The light-emitting device according to claim 11, wherein thefirst optical path length is one-quarter of a first central wavelengthof the first wavelength range, wherein the second optical path length isthree-quarters of a second central wavelength of the second wavelengthrange, wherein the third optical path length is five-quarters of a thirdcentral wavelength of the third wavelength range, and wherein the firstcentral wavelength is longer than the second central wavelength, andwherein the second central wavelength is longer than the third centralwavelength.
 13. The light-emitting device according to claim 11, whereinthe second light-emitting element further comprises a first conductivelayer having a light-transmitting property between the second electrodeand the first light-emitting layer, wherein the third light-emittingelement further comprises a second conductive layer having alight-transmitting property between the third electrode and the firstlight-emitting layer, and wherein the first conductive layer has adifferent thickness from the second conductive layer.
 14. Thelight-emitting device according to claim 13, wherein the firstconductive layer comprises a material selected from a group consistingof indium oxide, indium tin oxide, an indium oxide-zinc oxide alloy,zinc oxide, zinc oxide to which gallium is added, graphene, polyanilineor a derivative thereof, polypyrrole or a derivative thereof,polythiophene or a derivative thereof, and a copolymer of two or more ofaniline, pyrrole, and thiophene or a derivative thereof, and wherein thesecond conductive layer comprises a material selected from a groupconsisting of indium oxide, indium tin oxide, an indium oxide-zinc oxidealloy, zinc oxide, zinc oxide to which gallium is added, graphene,polyaniline or a derivative thereof, polypyrrole or a derivativethereof, polythiophene or a derivative thereof, and a copolymer of twoor more of aniline, pyrrole, and thiophene or a derivative thereof. 15.The light-emitting device according to claim 13, wherein the firstlight-emitting element further comprises a third conductive layer havinga light-transmitting property between the first electrode and the firstlight-emitting layer, and wherein the third conductive layer has adifferent thickness from the first conductive layer and the secondconductive layer.
 16. The light-emitting device according to claim 15,wherein the third conductive layer comprises a material selected from agroup consisting of indium oxide, indium tin oxide, an indium oxide-zincoxide alloy, zinc oxide, zinc oxide to which gallium is added, graphene,polyaniline or a derivative thereof, polypyrrole or a derivativethereof, polythiophene or a derivative thereof, and a copolymer of twoor more of aniline, pyrrole, and thiophene or a derivative thereof. 17.The light-emitting device according to claim 13, further comprising acharge generation layer between the first light-emitting layer and thesecond light-emitting layer, wherein the second light-emitting layer isin contact with the third light-emitting layer, wherein a spectrum oflight emitted from the first light-emitting layer has a peak in a rangeof 600 nm to 700 nm, wherein a spectrum of light emitted from the secondlight-emitting layer has a peak in a range of 520 nm to 550 nm, andwherein a spectrum of light emitted from the third light-emitting layerhas a peak in a range of 430 nm to 470 nm.
 18. The light-emitting deviceaccording to claim 13, further comprising an electrode having alight-transmitting property over the third light-emitting layer.
 19. Thelight-emitting device according to claim 11, wherein the first opticalpath length is an optical path length between a surface of the firstelectrode and a lower surface of the first light-emitting layer or moreand an optical path length between the surface of the first electrodeand an upper surface of the first light-emitting layer or less, whereinthe second optical path length is an optical path length between asurface of the second electrode and a lower surface of the secondlight-emitting layer or more and an optical path length between thesurface of the second electrode and an upper surface of the secondlight-emitting layer or less, and wherein the third optical path lengthis an optical path length between a surface of the third electrode and alower surface of the third light-emitting layer or more and an opticalpath length between the surface of the third electrode and an uppersurface of the third light-emitting layer or less.
 20. Thelight-emitting device according to claim 11, wherein the light-emittingdevice is a display device.
 21. The light-emitting device according toclaim 1, wherein the visible light range is 380 nm to 680 nm
 22. Thelight-emitting device according to claim 11, wherein the visible lightrange is 380 nm to 680 nm.